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

Infrared radiation from synchrotron storagerings serves as a high-brightness source fordiffraction-limited microspectroscopy inboth the mid- and far-infrared spectralranges. Mid-infrared absorption, due to localvibrational modes within complex molecules,is shown to be sensitive to small chemicalchanges associated with certain diseases.Farinfrared modes are believed to result from thefolding or twisting of larger, morecomplex molecules. The ability for thesynchrotron source to perform microscopy ata frequency of 1 THz is demonstrated.

Terahertz (THz) radiation, which lies in the far-infrared region, is at the interface of electronics and photonics. Narrow-band THz radiation can be produced by free-electron lasers and fast diodes. Broadband THz radiation can be produced by thermal sources and, more recently, by table-top laser-driven sources and by short electron bunches in accelerators, but so far only with low power. Here we report calculations and measurements that confirm the production of high-power broadband THz radiation from subpicosecond electron bunches in an accelerator. The average power is nearly 20 watts, several orders of magnitude higher than any existing source, which could enable various new applications. In particular, many materials have distinct absorptive and dispersive properties in this spectral range, so that THz imaging could reveal interesting features. For example, it would be possible to image the distribution of specific proteins or water in tissue, or buried metal layers in semiconductors; the present source would allow full-field, real-time capture of such images. High peak and average power THz sources are also critical in driving new nonlinear phenomena and for pump-probe studies of dynamical properties of materials.

A new genus and species in the eucalypt group of the Myrtaceae is described. Stockwellia quadrifida D.J. Carr, S.G.M. Carr & B.Hyland gen. et sp. nov. is a rainforest tree of restricted distribution on the Atherton Tableland, North Queensland, Australia. Molecular data suggest that it is the sister taxon to Eucalyptopsis and this is supported by morphological characters. The prolonged hypanthium and reduced perianth appear to be synapomorphies for these two genera and the circumscissile hypanthium a synapomorphy shared with Allosyncarpia. Stockwellia differs from Eucalyptopsis by the distinct, albeit reduced, perianth and the hypanthium splitting into four segments at anthesis. The relationship of these two genera indicates an historical biogeographical link between New Guinea and the Queensland wet tropics region. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 139, 415–421.

We measured the spectroscopic response of stripe- and vortex-containing ${\mathrm{ErMnO}}_{3}$ in order to uncover the electronic properties of the domain walls. We quantify Born effective charge and polarization differences using the lattice behavior, analyze the local rare earth environment from the $f$-manifold excitations, and reveal how shifts in the charge transfer excitations impact the band gap. The increased Born charge, polarization, and band gap in the vortex-containing material are brought together with a discussion of hybridization and wall density effects. The domain wall optical constants are strongly frequency dependent.

The characteristics of topological insulators are manifested in both their surface and bulk properties, but the latter remain to be explored. Here we report bulk signatures of pressure-induced band inversion and topological phase transitions in ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}\mathrm{Se}$ ($x=0.00$, 0.15, and 0.23). The results of infrared measurements as a function of pressure indicate the closing and the reopening of the band gap as well as a maximum in the free carrier spectral weight. The enhanced density of states near the band gap in the topological phase gives rise to a steep interband absorption edge. The change of density of states also yields a maximum in the pressure dependence of the Fermi level. Thus, our conclusive results provide a consistent picture of pressure-induced topological phase transitions and highlight the bulk origin of the novel properties in topological insulators.

Optical properties of hexagonal multiferroic oxides RMnO3 ,w hereR = Ho, Er, Tm, Yb, and Lu, have been studied in the far-infrared spectral range between 100 and 2000 cm −1 and temperatures between 1.5 and 300 K by means of several experimental techniques: Mueller matrix spectroscopic ellipsometry, rotating analyzer ellipsometry, and optical transmission spectroscopy. Spectra of the optical phonons are described in terms of the temperature dependencies of their frequency, damping, and oscillator strength. For all studies, oxide materials’ clear signatures of the spin-phonon interaction have been found below the temperature of the antiferromagnetic phase transition TN due to magnetic ordering of Mn 3+ spins. A decrease of the ionic radius for R 3+ ions between Ho 3+ and Lu 3+ in the corresponding RMnO3 compounds resulted in systematic variation of the frequency for several optical phonons. A magnetic excitation at 190 cm −1 was observed at low temperatures below TN and interpreted as resulting from two-magnon absorption.

Synopsis Synchrotron-based infrared microscopic measurements have been performed on various hair transverse sections, sampled either from the heads of Caucasian or Afro-American subjects. Lipid content of various virgin hair transverse sections was established, with an unprecedented resolution. The variations in shape and intensity of the CH2, CH3, amide I and amide II bands, before and after lipid removal by solvent extraction, were profiled, showing clearly that Caucasian hair often contains lipids localized inside the medulla and to a lesser extent inside the cuticle. This statement does not hold for the Afro-American hair analysed. For this, the FT-IR spectra do not change within the hair section and are insensitive to solvent extraction. The importance of the origin of hair on its physical and chemical properties has to be taken into account in future investigations. Resume Par utilisation de la microscopie infra-rouge utilisant le rayonnement synchrotron, la repartition des lipides sur la section de cheveux vierges (caucasiens et afro-americains), a pu etre comparee avec une resolution spatiale jamais egalee. La forme et l'intensite des bandes CH2, CH3, amide I et amide II, avant et apres delipidation par solvants ont ete obtenues. Il apparait que pour le cheveu caucasien, les lipides sont majoritairement localises dans la medule et dans la cuticule en quantite moindre. Ceci n'est pas le cas pour les cheveux afro-americains: leur spectre infra-rouge est le meme sur toute la section et est insensible a la delipidation. L'origine des cheveux est donc particulierement importante pour l'etude de leurs proprietes physico-chimiques.

OBJECTIVE—To dissociate the effect of inotropy from activation change during dobutamine stress on left ventricular long axis function in patients with coronary artery disease (CAD). METHODS—25 patients with CAD and normal left ventricular cavity size and 30 with cavity dilatation—18 with normal activation (DCM-NA) and 12 with left bundle branch block (DCM-LBBB)—were compared with 20 controls. 12 lead ECG and septal long axis echograms were assessed at rest and peak dobutamine stress. Amplitude, shortening and lengthening velocities, postejection shortening, Q wave to onset of shortening (Q-OS), and A2 to onset of lengthening (A2-OL) were measured. Inotropy was evaluated from peak aortic acceleration. RESULTS—In controls, amplitude, shortening and lengthening velocities, and peak aortic acceleration increased with stress; QRS, Q-OS, and A2-OL shortened (all p

We report the temperature-dependent infrared spectra of pure, deuterated, Zn-doped, and 2,6-dimethyl-substituted samples of the S = 1/2, one-dimensional Quantum Heisenberg Antiferromagnet (QHAF) copper pyrazine dinitrate (Cu(C4H4N2)(NO3)2). Of the more than 100 vibrational modes observed in the spectra, nearly one-third of them unexpectedly soften throughout the temperature range of investigation (300−5 K). We discuss the temperature dependence of the vibrational spectra in terms of several different models for mode softening. On the basis of detailed structural information and a comparison of the infrared spectra between pure copper pyrazine dinitrate and its chemically modified relatives, we conclude that the unusual softening observed in this low-dimensional molecular magnet is due to enhanced interchain hydrogen bonding with decreasing temperature.

We report the observation of multiparticle coherent emission in the very far infrared from bunched electrons in an electron storage ring. The emission occurs in quasi-periodic bursts, and only when the electron beam current exceeds a threshold value, suggesting an instability-driven modulation of the electron bunch density. For the operating conditions reported, the spectral content of the coherent emission is peaked near a wavelength of 7 mm. This wavelength is much shorter than the nominal electron bunch length, indicating the presence of a density modulation within the bunch.

(2000). The impact of infrared synchrotron radiation in biology: Past, present and future. Synchrotron Radiation News: Vol. 13, No. 5, pp. 31-38.

The instrumentation and performance of the new infrared beamline U12IR at the National Synchrotron Light Source of Brookhaven National Laboratory is described. This beamline utilizes infrared synchrotron radiation from a bending magnet. A combination of beamline design features and spectroscopic instrumentation allows the facility to reach the extremely low frequency limit of ∼2 cm−1 (i.e., 60 GHz or a photon energy of 250 μeV). The infrared light from the synchrotron emission at U12IR is compared to standard thermal sources and reveals substantial benefits for the study of small samples. In particular, the intensity of the synchrotron radiation in the far infrared can be as much as 200 times greater than that from a blackbody when millimeter-sized samples are measured. The effects of diffraction and noise on beamline performance are also discussed.

A Bruker model IFS 125HR Fourier transform interferometer has been installed and its performance tested using high-brightness, far-infrared synchrotron radiation. Results of absorption measurements for the rotational modes of water vapor demonstrate a nearly 10-fold improvement in signal-to-noise when compared with the instrument’s internal high-pressure Hg arc lamp source.

The potentiality of synchrotron infrared microspectrometry was investigated for in situ analysis of fluid inclusions and volatiles of particular geological interest. Thanks to the intrinsic high brightness of the synchrotron infrared source, areas as small as a few μm2 can be probed, providing a high-contrast analysis of small inclusions in geological materials. We have identified organic components in such small volumes in their liquid and gaseous phase, thus allowing a deeper analysis of oil-water inclusions entrapped in diagenetic cements. Such detailed analysis opens up new perspectives in petroleum reservoir evolution studies. The high signal-to-noise ratio of spectra obtained in small volume allows a fast and accurate chemical mapping of the inclusion components. Drastic refraction effects preclude, at the present state, a quantitative analysis of either the volume or the thickness of the individual inclusions. Traces of volatiles such as CO2 and H2O are easily detected in the vitreous and gaseous part of the glass melt fluid inclusions. We have also profiled the hydroxyl concentration near a wall, and calculated the hydrogen diffusion coefficient in anhydrous minerals such as diopside.

We review the properties of infrared synchrotron radiation and particularly those of the beamlines at the NSLS, Brookhaven National Laboratory. We show how this unique, pulsed broadband source with its 1000-fold brightness advantage over thermal sources has been utilized for research programs in surface science, solid-state physics and microscopy and discuss plans for 5 new beamlines at the NSLS.

The high brightness, broad spectral coverage and pulsed characteristics of infrared synchrotron radiation enable time-resolved spectroscopy under throughput-limited optical systems, as can occur with the high-field magnet cryostat systems used to study electron dynamics and cyclotron resonance by far-infrared techniques. A natural extension for magnetospectroscopy is to sense circular dichroism, i.e. the difference in a material’s optical response for left and right circularly polarized light. A key component for spectroscopic circular dichroism is an achromatic 1 4 wave retarder functioning over the spectral range of interest. We report here the development of an in-line retarder using total internal reflection in high-resistivity silicon. We demonstrate its performance by distinguishing electronic excitations of differing handedness for GaAs in a magnetic field. This 1 4 wave retarder is expected to be useful for far-infrared spectroscopy of circular dichroism in many materials.

The immunosuppressive activity of human seminal plasma may be one factor in the aetiology of sexually transmitted disease and could be particularly important for the spread of human immunodeficiency virus (HIV). The advent of virus that can preferentially infect Langerhans cells of the genital mucosa underscores the relevance of seminal plasma effects. Virally infected cells are eradicated by the killing activity of T cells and natural killer (NK) cells and this cytotoxicity is stimulated by IL-12 (previously known as natural killer cell stimulatory factor) and partly inhibited by IL-10 (previously known as cytokine synthesis inhibitory factor). We have examined the effects of human seminal plasma on the production of these key cytokines. Cytokine production was measured in rapidly diluted, fresh, lipopolysaccharide (LPS)-stimulated, whole blood since this provided leukocytes with minimal exposure to prostaglandin. Prostaglandin concentrations and cytokine release were measured by ELISA. Addition of human seminal plasma diluted up to 100 000 times (0.001%) to blood cell cultures led to a marked increase in the IL-10/IL-12 ratio (P

We report the observation of two signatures of a pressure-induced topological quantum phase transition in the polar semiconductor BiTeI using x-ray powder diffraction and infrared spectroscopy. The x-ray data confirm that BiTeI remains in its ambient-pressure structure up to 8 GPa. The lattice parameter ratio c/a shows a minimum between 2.0-2.9 GPa, indicating an enhanced c-axis bonding through pz band crossing as expected during the transition. Over the same pressure range, the infrared spectra reveal a maximum in the optical spectral weight of the charge carriers, reflecting the closing and reopening of the semiconducting band gap. Both of these features are characteristics of a topological quantum phase transition, and are consistent with a recent theoretical proposal., revised final version

High contrast imaging can use pupil apodizers to suppress diffracted starlight from a bright source in order to observe its environs. Metallic half-tone dot transmissive apodizers were developed for the Gemini Planet Imager (GPI) and ESO SPHERE coronagraphs for use in the near-IR. Dot sizes on the scale of the wavelength of the light often result in unexpected variations in the optical transmission vs. superficial dot density relation. We measured 5 and 10 micron half-tone microdot screens' transmissions between 550 -1050 nm to prepare to fabricate apodizations that mitigate diffraction by segments gaps and spiders on future large space telescopes. We utilized slow test beams (f/40, f/80) to estimate the on-axis (far-field, or zero-order) transmission of test patches using a Fourier Transform Spectrograph on Beamline U10B at Brookhaven National Laboratory's National Synchrotron Light Source (BNL NSLS). We also modified our previous GPI IR characterization hardware and methods for this experiment. Our measurements show an internal consistency of 0.1% in transmission, a factor of 5 better than our near-IR GPI work on the NSLS U4IR beamline. The systematics of the set-up appeared to limit the absolute calibration for our f/40 data on the 50-patch, maximum Optical Density 3 (OD3), sample. Credible measurements of transmissions down to about 3% transmission were achieved for this sample. Future work on apodizers for obstructed and segmented primary mirror coronagraphs will require configurations that mimic the intended diffractive configurations closely in order to tune apodizer fabrication to any particular application, and measure chromatic effects in representative diffractive regimes. Further experimental refinements are needed to measure the densest test patches which possess transmissions less than a few percent. The new NSLS-II should provide much greater spectral stability of its synchrotron beam, which will improve measurement accuracy and reduce systematics.

Vanadium dioxide (VO2) undergoes a phase transition at a temperature of 340 K between an insulating monoclinic M1 phase and a conducting rutile phase. Accurate measurements of possible anisotropy of the electronic properties and phonon features of VO2 in the insulating monoclinic M1 and metallic rutile phases are a prerequisite for understanding the phase transition in this correlated system. Recently, it has become possible to grow single domain untwinned VO2 microcrystals which makes it possible to investigate the true anisotropy of VO2. We performed polarized transmission infrared micro-spectroscopy on these untwinned microcrystals in the spectral range between 200 cm-1 and 6000 cm-1 and have obtained the anisotropic phonon parameters and low frequency electronic properties in the insulating monoclinic M1 and metallic rutile phases. We have also performed ab initio GGA+U total energy calculations of phonon frequencies for both phases. We find our measurements and calculations to be in good agreement., 19 pages, 7 figures, 4 tables

Reflection and transmission as a function of temperature (7-300 K and 5-300 K respectively) have been measured on single crystals of the multiferroic compound FeTe2O5Br utilizing light spanning from the far infrared to the visible. The complex dielectric function and other optical properties were obtained via Kramers-Kronig analysis and by fits to a Drude-Lortentz model. Analysis of the anisotropic excitation spectra via Drude-Lorentz fitting and lattice dynamical calculations have led to the observation of 43 of the 53 modes predicted along the b axis of the monoclinic cell. The phonon response parallel to the a and c axes are also presented. Assignments to groups (clusters) of phonons have been made and trends within them are discussed in light of our calculated displacement patterns.

The vortex-state electrodynamics of s-wave superconductors has been studied by infrared spectroscopy. Far-infrared transmission and reflection spectra of superc onducting Nb0.5Ti0.5N and NbN thin films were measured in a magnetic field perpendicular to the film surface , and the optical conductivity was extracted. The data show clear reduction of superconducting signature. We consider the vortex state as a twocomponent effective medium of normal cores embedded in a BCS superconductor. The spectral features are well explained by the Maxwell-Garnett theory. Our analysis supports the presence of magnetic-fieldinduced pair-breaking effects in the superconducting component outside of the vortex cores. The vortex or Abrikosov state exists in type-II superconductors subjected to magnetic fields between Bc1 and Bc2. In this state the field penetrates the superconductor in the form of quantized tubes of flux, or vortices. The superconducting gap is zero inside the vortex cores and finite outside so that each vortex may be considered to have a core of normal metal, surrounded by superconductor [1, 2]. Because vortex quantization renders the material an inhomogeneous system, it necessarily affects the electrodynamics of the s uperconductor. The microwave response of the vortex state has been extensively studied theoretically [3‐5] and experimentally [6‐11]. However the picture is still incomplete in the infrared region spanning the superconducting gap [12, 13]. In this Letter we address the infrared electrodynamics of the vortex state. We obtain the complex optical conductivity of type-II superconductors and compare our results to calculations of a superconductor-normal metal mixture using the two key models for the effective conductivity of an inhomogeneous system: that of Garnett [14] (the so-called “Maxwell-Garnett theory” or MGT) and that of Bruggeman [15] (sometimes called the “effective-medium approximation” or EMA). We also compare our results to a theory of viscous motion of vortices driven by currents in the superconductor [3]. We find that only the MGT gives a good description of experiment, and then only when pairbreaking by the magnetic field [16‐18] is considered. That it does so is reasonable considering the topology of the vortex state: normal regions surrounded entirely by a connected superfluid. As pointed out some years ago [19], this is the topology of the MGT: the inclusions are embedded in a host medium and are correlated to stay apart. In contrast, the EMA allows percolation of the minority constituent at some critical concentration, something that does not happen in the vortex state until the upper critical field, when the entire material is in the normal state. We studied type-II superconducting thin films of BCS superconductors Nb0.5Ti0.5N and NbN, which are widely used in superconducting magnets [20], RF cavities [21], and photodetectors [22]. The 10 nm Nb0.5Ti0.5N film was grown on a quartz substrate in Ar and N2 gas with a NbTi target, and the 70 nm NbN film grown on a MgO substrate in N2 atmosphere using Nb, both by reactive magnetron sputtering [23, 24]. The substrates have negligible absorption in the spectral range of interest (10‐ 100 cm −1 ) for T < 20 K. We performed the experiment at Beamline U4IR of the National Synchrotron Light Source, Brookhaven National Laboratory. The beamline is equipped with a Bruker IFS 66v FT-IR spectrometer, modified to use synchrotron radiation and a superconducting magnet for low-temperature magneto-spectroscopy. A composite silicon bolometer operating at T ∼1.5 K detects far-infrared radiation with high sensitivity. Both sample s were cooled to 2 K (≪ Tc) in zero field, and their transmission and reflection measured in magnetic fields from 0‐10 T, with the field direction normal to the sample sur

Microspectroscopic imaging in the infrared (IR) spectral region allows for the examination of spatially resolved chemical composition on the microscale. More than a decade ago, it was demonstrated that diffraction limited spatial resolution can be achieved when an apertured, single pixel IR microscope is coupled to the high brightness of a synchrotron light source. Nowadays, many IR microscopes are equipped with multi-pixel Focal Plane Array (FPA) detectors, which dramatically improve data acquisition times for imaging large areas. Recently, progress been made toward efficiently coupling synchrotron IR beamlines to multi-pixel detectors, but they utilize expensive and highly customized optical schemes. Here we demonstrate the development and application of a simple optical configuration that can be implemented on most existing synchrotron IR beamlines in order to achieve full-field IR imaging with diffraction-limited spatial resolution. Specifically, the synchrotron radiation fan is extracted from the bending magnet and split into four beams that are combined on the sample, allowing it to fill a large section of the FPA. With this optical configuration, we are able to oversample an image by more than a factor of two, even at the shortest wavelengths, making image restoration through deconvolution algorithms possible. High chemical sensitivity, rapid acquisition times, and superior signal-to-noise characteristics of the instrument are demonstrated. The unique characteristics of this setup enabled the real time study of heterogeneous chemical dynamics with diffraction-limited spatial resolution for the first time.

The far-infrared (30--350 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) transmittance and reflectance of two ab-plane-oriented ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ films have been measured. These data show that the quasiparticle relaxation rate, 1/\ensuremath{\tau}, has a fast decrease below ${\mathit{T}}_{\mathit{c}}$ and saturates at T\ensuremath{\ll}${\mathit{T}}_{\mathit{c}}$. Above ${\mathit{T}}_{\mathit{c}}$, 1/\ensuremath{\tau} exhibits a linear temperature dependence, in accord with the linear dc resistivity in the normal state. The fast decrease of 1/\ensuremath{\tau} is unique and intrinsic to the high-${\mathit{T}}_{\mathit{c}}$ cuprates; it does not occur in conventional BCS superconductors, where the scattering is from impurity or phonons. The low-frequency conductivity ${\mathrm{\ensuremath{\sigma}}}_{1}$ inferred from the far-infrared transmittance and reflectance measurements exhibits a peak just below ${\mathit{T}}_{\mathit{c}}$. The conductivity peak occurs at higher frequencies than those expected for BCS coherence effects. The peak in ${\mathrm{\ensuremath{\sigma}}}_{1}$ is attributed to the rapid drop in 1/\ensuremath{\tau} combined with a decreasing normal-fluid density. \textcopyright{} 1996 The American Physical Society.

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

Although it is known that concentrations of immunoreactive ACTH increase during late gestation in fetal sheep plasma, the nature of the ACTH has not been well characterized. We used two-site immunoradiometric assays to separately measure high mol wt ACTH precursors (POMC and pro-ACTH) and ACTH-(1-39) in plasma of fetal sheep with chronic arterial and venous catheters. We compared the ratio of these peptides as a function of gestational age under basal conditions and in response to exogenous vasopressin and/or corticotropin-releasing hormone. Under basal conditions, the concentration of precursors was not changed throughout the last third of gestation; however, ACTH-(1-39) increased significantly approaching term. The molar ratio of precursors to ACTH-(1-39), therefore, decreased from 15.8 +/- 1.0 at 110 days to 7.9 +/- 0.6 at 140 days gestation. At all gestational ages, vasopressin and corticotropin-releasing hormone increased ACTH-(1-39) and precursors, albeit with different time courses. At 120 days gestation, arginine vasopressin plus CRH produced synergistic increases in ACTH-(1-39) and precursors, whereas the response was only additive at other ages. The present results indicate that the elevation in the resting plasma immunoreactive ACTH concentration that occurs near term is constituted by an increase in the concentration of ACTH-(1-39) relative to those of POMC and pro-ACTH, which may have further physiological significance. Also, CRH and AVP are potent stimulators of both ACTH-(1-39) and ACTH precursors.

Infrared reflection and transmission as a function of temperature have been measured on single crystals of Cu3Bi(SeO3)(2)O2Cl. The complex dielectric function and optical properties along all three principal axes of the orthorhombic cell were obtained via Kramers-Kronig analysis and by fits to a Drude-Lorentz model. Below 115 K, 16 additional modes [8(E parallel to(a) over cap)+ 6(E parallel to(b) over cap)+ 2(E parallel to(c) over cap)] appear in the phonon spectra; however, powder x-ray diffraction measurements do not detect a new structure at 85 K. Potential explanations for the new phonon modes are discussed. Transmission in the far infrared as a function of temperature has revealed magnetic excitations originating below the magnetic ordering temperature (T-c similar to 24 K). The origin of the excitations in the magnetically ordered state will be discussed in terms of their response to different polarizations of incident light, behavior in externally applied magnetic fields, and the anisotropic magnetic properties of Cu3Bi(SeO3)(2)O2Cl as determined by dc susceptibility measurements.

Optical conductivity [{delta}({omega})] of PrRu{sub 4}P{sub 12} has been studied under high pressure to 14 GPa, at low temperatures to 8 K, and at photon energies 12 meV-1.1 eV. The energy gap in {delta}({omega}) at ambient pressure, caused by a metal-insulator transition due to an unconventional charge-density-wave formation at 63 K, is gradually filled in with increasing pressure to 10 GPa. At 14 GPa and below 30 K, {delta}({omega}) exhibits a pronounced Drude-type component due to free carriers. This indicates that the initial insulating ground state at zero pressure has been turned into a metallic one at 14 GPa. This is consistent with a previous resistivity study under pressure, where the resistivity rapidly decreased with cooling below 30 K at 14 GPa. The evolution of electronic structure with pressure is discussed in terms of the hybridization between the 4f and conduction electrons.

We demonstrate the generation of tunable, narrow-band, few-cycle and multi-cycle terahertz pulses from a temporally modulated relativistic electron beam through coherent transition radiation. OCIS codes: 320.0320

Quasiparticle recombination in a superconductor with an s-wave gap is typically dominated by a phonon bottleneck effect. We have studied how a magnetic field changes this recombination process in metallic thin-film superconductors, finding that the quasiparticle recombination process is significantly slowed as the field increases. While we observe this for all field orientations, we focus here on the results for a field applied parallel to the thin film surface, minimizing the influence of vortices. The magnetic field disrupts the time-reversal symmetry of the pairs, giving them a finite lifetime and decreasing the energy gap. The field could also polarize the quasiparticle spins, producing different populations of spin-up and spin-down quasiparticles. Both processes favor slower recombination; in our materials we conclude that strong spin-orbit scattering reduces the spin polarization, leaving the field-induced gap reduction as the dominant effect and accounting quantitatively for the observed recombination rate reduction.

We report the generation of tunable, narrow-band, few-cycle and multicycle coherent terahertz (THz) pulses from a temporally modulated relativistic electron beam. We demonstrate that the frequency of the THz radiation and the number of the oscillation cycles of the THz electric field can be tuned by changing the modulation period of the electron beam through a temporally shaped photocathode drive laser. The central frequency of the THz spectrum is tunable from $\ensuremath{\sim}0.26$ to 2.6 THz with a bandwidth of $\ensuremath{\sim}0.16\text{ }\text{ }\mathrm{THz}$.

We report the generation and characterization of single-, few-, and multi-cycle terahertz pulses from relativistic electrons.

The in-plane optical phonons around 200 meV in few-layer graphene are investigated utilizing infrared absorption spectroscopy. The phonon spectra exhibit unusual asymmetric features characteristic of Fano resonances, which depend critically on the layer thickness and stacking order of the sample. The phonon intensities in samples with rhombohedral (ABC) stacking are significantly higher than those with Bernal (AB) stacking. These observations reflect the strong coupling between phonons and interband electronic transitions in these systems and the distinctive variation in the joint density of electronic states in samples of differing thickness and stacking order., 20 pages, 7 figures, supplementary material included

Hybridization between Dubautia ciliolata and D. scabra occurring on a mosaic of lava flows of 1855 and 1935 on the island of Hawai'i was examined using random amplified polymorphic DNA (RAPD) markers. The RAPD data indicate that D. ciliolata plants, nearly restricted to the 1855 lava flow, contain higher levels of genetic variation than do D. scabra plants occurring on the 1935 lava flow. Seventy-one markers were specific to D. ciliolata and 60 to D. scabra; 40 of these were "constant" (found in all individuals) in one or the other species. Hybrids sampled were determined to represent F(1), filial hybrids beyond the F(1), and backcross progeny. All backcrosses were unidirectional with D. ciliolata acting as the recurrent parent. No hybrid, including an artificially produced F(1), had all 40 constant markers, suggesting that at least some loci for these markers were heterozygous in the parents. However, several hybrids exhibited a loss of many of the species markers, suggesting that they were later filial hybrid generation plants. The apparent occurrence of unidirectional introgression at the study site may be providing D. ciliolata plants with genetic plasticity to colonize the new lava flow previously occupied only by D. scabra.

The VUV ring at the National Synchrotron Light Source (NSLS, Brookhaven national Laboratory) is a source of nanosecond-duration, high-brightness, broadband IR pulses. The authors are developing several measurement techniques for characterizing Hg1-xCdxTe and other IR detector materials using this source. For example, the broadband IR pulses can be used to study transient photoconductive decay at various photon energies near the bandgap. A particularly novel technique they have developed is far-infrared photoinduced nanosecond spectroscopy (FIR-PINS). In this all-optical (contactless) measurement, a short laser pulse generates photocarriers which are subsequently sensed by a far-infrared pulse from the synchrotron. Spectroscopic analysis of the far-infrared yields the free carrier plasma frequency, providing information on the photocarrier density. By varying the delay time of the far-infrared pulse (relative to the laser pulse), the photocarrier relaxation is determined with nanosecond resolution. In addition to being contactless, the technique offers other potential advantages over electrical measurements. Results for MBE-grown Hg1-xCdxTe are presented.

We report the complex optical conductivity of a superconducting thin film of Nb 0.5 Ti 0.5 N in an external magnetic field. The field was applied parallel to the film surface and the conductivity extracted from far-infrared transmission and reflection measurements. The real part shows the superconducting gap, which we observe to be suppressed by the applied magnetic field. We compare our results with the pair-breaking theory of Abrikosov and Gor'kov and confirm directly the theory's validity for the optical conductivity.

In this chapter we consider developments in the use of infrared (IR) synchrotron radiation for microspectroscopy based on instruments having two-dimensional (2D) array detectors. As with microspectroscopy using single-element detectors (SEDs), we anticipate that the IR synchrotron radiation source i...

We report the complex optical conductivity of a superconducting thin film of Nb 0.5 Ti 0.5 N in an external magnetic field. The field was applied parallel to the film surface and the conductivity extracted from far-infrared transmission and reflection measurements. The real part shows the superconducting gap, which we observe to be suppressed by the applied magnetic field. We compare our results with the pair-breaking theory of Abrikosov and Gor'kov and confirm directly the theory's validity for the optical conductivity.

The Gemini Planet Imager (GPI) is an extreme AO coronagraphic integral field unit YJHK spectrograph destined for first light on the 8m Gemini South telescope in 2011. GPI fields a 1500 channel AO system feeding an apodized pupil Lyot coronagraph, and a nIR non-common-path slow wavefront sensor. It targets detection and characterizion of relatively young (

We demonstrate that an intense single-cycle terahertz (THz) pulse can act as a time lens to phase modulate and compress a copropagating ultrashort laser pulse. By using the THz-induced phase modulation as a time lens and a glass plate as a group velocity dispersive element, we have compressed an unchirped $~165$ fs laser pulse to $~45$ fs.

We demonstrate that an intense subpicosecond single-cycle terahertz pulse in an electro-optic medium can act as a temporal and spatial lens to phase modulate and focus a co-propagating ultrashort laser pulse.

International audience; We have measured the low-energy excitonic transitions of chiral assigned individual large-diameter semiconducting single-walled nanotubes using a high-resolution Fourier transform photoconductivity technique. When photoconductivity is complemented by Rayleigh scattering spectroscopy, as many as five optical transitions can be identified on the same individual nanotube over an energy range of 0.3-2.7 eV. We find that well-established energy scaling relations developed for nanotubes of smaller diameter are not consistent with the measured low-energy transitions in large (1.8-2.3 nm) diameter nanotubes.

The infrared absorption of oxide superconductors will be discussed. In the normal state, σ 1 (ω) consists of a strongly T -dependent part in the far infrared, above which is a weakly- T -dependent midinfrared absorption. In the superconducting state, there is absorption to very low frequencies, well below where the superconducting gap is expected to be. It is argued that this absorption is due to a second (“midinfrared”) component which is only weakly affected by the onset of superconductivity. The free carrier component is in the clean limit and most of its oscillator strength goes into the superfluid condensate zero-frequency delta function response.

The response of a granular film of YBa 2.1 Cu 3.4 O 7-x to pulsed far-infrared light has been measured at temperatures which are near the resistive onset of the film. The photoresponse at 26.0 cm -1 is interpreted due to the direct modulation of intergrain Josephson currents (current mode) by the incident far-infrared light. The observed dependence on far-infrared power (∼P 1/2 ) is consistent with a superconducting energy gap which is much larger than 26.0 cm -1