Performance with various diffraction gratings:

Outline Drawing

Select Publications

Luminescence signature of free exciton dissociation and liberated electron transfer across the junction of graphene/GaN hybrid structure (NATURE)

Abstract: Read at NATURE website Large-area graphene grown on Cu foil with chemical vapor deposition was transferred onto intentionally undoped GaN epilayer to form a graphene/GaN Schottky junction. Optical spectroscopic techniques including steady-state and time-resolved photoluminescence (PL) were employed to investigate the electron transfer between graphene and n-type GaN at different temperatures. By comparing the near-band-edge excitonic emissions before and after the graphene covering, some structures in the excitonic PL spectra are found to show interesting changes. In particular, a distinct “dip” structure is found to develop at the center of the free exciton emission peak as the temperature goes up. A mechanism that the first dissociation of some freely moveable excitons at the interface was followed by transfer of liberated electrons over the junction barrier is proposed to interpret the appearance and development of the “dip” structure. The formation and evolution process of this “dip” structure can be well resolved from the measured time-resolved PL spectra. First-principles simulations provide clear evidence of finite electron transfer at the interface between graphene and GaN.

Jun Wang, Changcheng Zheng, Jiqiang Ning, Lixia Zhang, Wei Li, Zhenhua Ni, Yan Chen, Jiannong Wang & Shijie Xu

Hollow-core photonic crystal fiber-optic probes for Raman spectroscopy

Abstract: We have implemented a new Raman fiber-optic probe design based on a hollow-core photonic-crystal excitation fiber surrounded by silica-core collection fibers. The photonic-crystal fiber offers low attenuation at the pump radiation wavelength, mechanical flexibility, high radiation stability, and low background noise. Because the excitation beam is transmitted through air inside the hollow-core fiber, silica Raman scattering is much reduced, improving the quality of the spectra obtained using probes of this design. Preliminary results show that the new probe design decreases the Raman background from the silica by approximately an order of magnitude compared to solid-core silica Raman probes.

Stanislav O. Konorov, Christopher J. Addison, H. Georg Schulze, Robin F. B. Turner, and Michael W. Blades

Radial excitation temperatures in argon-nitrogen inductively coupled plasmas

Abstract: Abel-inverted excitation temperatures are measured for Ar-N2 inductively coupled plasmas (ICPs) formed in a conventional torch using a 27.12-MHz crystal-controlled generator. The dependence of temperature on gas composition (0–100% N2 in the outer flow), forward power (1.2–3.0 kW), observation height (6 and 15 mm) and injector gas flow-rate (1 and 2 l min–1) are studied using Fe as the thermometric species. When 5–10% N2 is used in the outer gas flow instead of pure Ar, the axial temperature is approximately 1000 K greater than that of the commonly used Ar ICP. Substitution of Ar in the outer flow by pure N2 reduces the axial temperature from 6200 to 4900 K at 1.2-kW forward power. At 2.5 kW, the Ar-N2 plasma, with pure N2 in the outer flow, exhibits a temperature of approximately 6200 K, similar to that of a 1.2-kW Ar ICP

Izumi Ishii, D. W. Golightly and Akbar Montaser

Capillary Electrophoresis-Fluorescence Line-Narrowing (CE-FLN) System for DNA Adduct Characterization

Abstract: Capillary electrophoresis (CE) interfaced with low-temperature (4.2 K) fluorescence line-narrowing (FLN) spectroscopy is used for separation and structural characterization of polycyclic aromatic hydrocarbon-derived DNA adducts. The CE-FLN system is applied to the separation and identification of mixtures of benzo[a]pyrene and dibenzo[a,l]pyrene DNA adducts. Interfacing CE with FLN spectroscopy allows on-line separation and high-resolution spectroscopic identification of CE-separated DNA adducts, providing a new powerful tool for DNA adduct structure characterization

R. Jankowiak, D. Zamzow, and G. J. Small

Temperature dependence of biexciton luminescence in cubic ZnS single crystals

Abstract: Temperature dependence of the excitonic and biexcitonic emissions in cubic ZnS single crystals has been studied by photoluminescence technique. We observed the very well-resolved excitonic and biexcitonic emissions from cubic ZnS single crystals with very low excitation density, in the tens-of-milliwatts-per-square-centimetre range. The kinetic energy contribution to the shift with temperature of the biexcitonic emission was determined showing a characteristic difference with the normal shift caused by the temperature-narrowed band gap.

N.Q Liem, V.X Quang, D.X Thanh, J.I Lee, D Kim

Multi-point, high-speed passive ion velocity distribution diagnostic on the Pegasus Toroidal Experiment

Abstract: A passive ion temperature polychromator has been deployed on Pegasus to study power balance and non-thermal ion distributions that arise during point source helicity injection. Spectra are recorded from a 1 m F/8.6 Czerny-Turner polychromator whose output is recorded by an intensified high-speed camera. The use of high orders allows for a dispersion of 0.02 Å/mm in 4th order and a bandpass of 0.14 Å (∼13 km/s) at 3131 Å in 4th order with 100 μm entrance slit. The instrument temperature of the spectrometer is 15 eV. Light from the output of an image intensifier in the spectrometer focal plane is coupled to a high-speed CMOS camera. The system can accommodate up to 20 spatial points recorded at 0.5 ms time resolution. During helicity injection, stochastic magnetic fields keep Te low (∼100 eV) and thus low ionization impurities penetrate to the core. Under these conditions, high core ion temperatures are measured (Ti ≈ 1.2 keV, Te ≈ 0.1 keV) using spectral lines from carbon III, nitrogen III, and boron IV

M. G. Burke, R. J. Fonck, M. W. Bongard, D. J. Schlossberg and G. R. Winz

A reflective optical transport system for ultraviolet Thomson scattering from electron plasma waves on OMEGA

Abstract: A reflective optical transport system has been designed for the OMEGA Thomson-scattering diagnostic. A Schwarzschild objective that uses two concentric spherical mirrors coupled to a Pfund objective provides diffraction-limited imaging across all reflected wavelengths. This enables the operator to perform Thomson-scattering measurements of ultraviolet (0.263 μm) light scattered from electron plasma waves

Katz J, Boni R, Sorce C, Follett R, Shoup MJ 3rd, Froula DH

Dynamic Stark Spectroscopic Measurements of Microwave Electric Fields Inside the Plasma Near a High-Power Antenna

Abstract: Fully dynamic Stark effect visible spectroscopy was used for the first time to directly measure the local rf electric field in the boundary plasma near a high-power antenna in high-performance, magnetically confined, fusion energy experiment. The measurement was performed in the superconducting tokamak Tore Supra, in the near field of a 1–3 MW, lower-hybrid, 3.7 GHz wave-launch antenna, and combined with modeling of neutral atom transport to estimate the local rf electric field amplitude (as low as 1–2  kV/cm) and direction in this region. The measurement was then shown to be consistent with the predicted values from a 2D full-wave propagation model. Notably the measurement confirmed that the electric field direction deviates substantially from the direction in which it is launched by the waveguides as it penetrates only a few cm radially inward into the plasma from the waveguides, consistent with the model

C. C. Klepper, R. C. Isler, J. Hillairet, E. H. Martin, L. Colas, A. Ekedahl, M. Goniche, J. H. Harris, D. L. Hillis, S. Panayotis, B. Pegourié, Ph. Lotte, G. Colledani, V. Martin, and Tore Supra Lower Hybrid Systems Technical Team

Direct, spectroscopic measurement of electric fields in a plasma-RF antenna interaction region in Tore Supra

Abstract: Balmer-series spectral line profiles of deuterium emission near a lower-hybrid (3.7 GHz) wave, high power (1–4 MW) launcher were measured with high-spectral resolution in the Tore Supra tokamak and fitted to an atomic physics model which includes both Zeeman and dynamic Stark effects. The magnetic field is static and the electric field is assumed to be monochromatic at 3.7 GHz. The determined strength and direction of the high-frequency electric field is found to be in good agreement with the results of a simulation that computes the propagation of these lower hybrid waves into the plasma in the region around the launch antenna and specifically in the region of estimated peak emission contributing to the measurement. This agreement indicates feasibility for the use of dynamic Stark effect spectroscopy to study interaction at the plasma antenna interactions in a fusion plasma environment

C.C. Klepper, D.L. Hillis, R.C. Isler, J. Hillairet, E.H. Martin, L. Colas, A. Ekedahl, M. Goniche, Ph. Lotte, G. Colledani, V. Martin, S. Panayotis, B. Pegourié, J.H. Harris

Measurement of the edge plasma rotation on J-TEXT tokamak

Abstract: A multi-channel high resolution spectrometer was developed for the measurement of the edge plasma rotation on J-TEXT tokamak. With the design of two opposite viewing directions, the poloidal and toroidal rotations can be measured simultaneously, and velocity accuracy is up to 1 km/s. The photon flux was enhanced by utilizing combined optical fiber. With this design, the time resolution reaches 3 ms. An assistant software “Spectra Assist” was developed for implementing the spectrometer control and data analysis automatically. A multi-channel monochromatic analyzer is designed to get the location of chosen ions simultaneously through the inversion analysis. Some preliminary experimental results about influence of plasma density, different magnetohydrodynamics behaviors, and applying of biased electrode are presented

Z. F. Cheng, J. Luo, Z. J. Wang, Z. P. Zhang, X. L. Zhang, S. Y. Hou, C. Cheng and G. Zhuang

Production of bright, wideband white light from Y 2 O 3 nano-powders induced by laser diode emission

Abstract: We report the production of efficient, wideband white light with a spectrum ranging from 400 to 900 nm obtained by using nominally un-doped Y2O3 nanopowders when excited with the 803.5 nm emission of a laser diode. The powders synthesized by using thermal decomposition technique were estimated to be 20 nm in size by using XRD patterns and confirmed of this size by using SEM images. The color temperature of the obtained white light was determined as 2756 K with a high color rendering index of 99.

Gökhan Bilir, Baldassare Di Bartolo

Visible spectroscopy measurements in the PBFA II (Particle Beam Fusion Accelerator) ion diode

Abstract: We describe a new visible spectroscopy diagnostic system for measuring plasma properties in the PBFA II applied-B ion diode. The system transports light from the ion diode to a remote screen room where it is recorded by a spectrography coupled to a streak camera. We developed extensive calibration techniques for measuring the collection efficiency into the fiber link, the effects of the background bremsstrahlung radiation on the fibers, the fiber transmission as a function of wavelength, and the absolute streaked-spectrograph sensitivity as a function of wavelength. We have recorded time-dependent spectral line profiles and intensities from the PBFA II plasma opening switch, the beam-transport gas cell, and the anode plasma. The Stark shift of the LiI 2s-2p transition observed on LiF-anode shots shows that the time-resolved electric field peaks at 7--8 MV/cm, the highest field ever measured using the Stark effect. The potential of these measurements to expand our knowledge of ion-diode physics is being explored.

J. Bailey, A.L. Carlson, R.L. Morrison, Y. Maron

HELIOS Diagnostic for the Prototype Material Plasma Exposure eXperiment

Abstract: A helium line-ratio spectral monitoring (HELIOS) diagnostic has been implemented on Oak Ridge National Laboratory's (ORNL) Prototype Material Plasma Exposure eXperiment (Proto-MPEX). A Filterscope and a 1 meter McPherson spectrometer are used to measure the intensity of three separate helium lines: 667.9 nm, 706.53 nm, and 728.0 nm. The open magnetic geometry of Proto-MPEX allows for direct comparison between the derived ne and Te values to nearby double Langmuir probes (DLP) and Thomson scattering (TS) measurements. Preliminary HELIOS measurements give Te values of 5 - 8 eV and density values of 2.71e18 m-3 - 9.34e18 m-3, which are consistent with edge Thomson Scattering Te and ne. The ability to measure the core density (>2.00e19 m-3) and low temperature (<5 eV) regime of Proto-MPEX with HELIOS is of great interest; however, the gas puff penetration into the plasma column is limited by the ne of the core. The gas puff was increased until signs of core gas penetration were observed. The data suggest that the high neutral helium density introduced to the chamber during the gas puff is causing radiation trapping of the ground state singlet transitions: 21P ->31D (667.9 nm) and 21P ->31S (728.0 nm). Correcting for this brings the HELIOS measured ne and Te in the core of the discharge into agreement with DLP measurements.

Ray, Holly; Biewer, Theodore; Caneses, Juan; Kafle, Nischal; Muñoz Burgos, Jorge M.; Unterberg, Ezekial; Schmitz, Oliver

Precision diagnostic system enhancements and recommissioning for advanced laser beam characterization at the National Ignition Facility

Abstract: The Precision Diagnostic System (PDS) is an advanced set of laser diagnostic tools installed within the National Ignition Facility (NIF). It is capable of picking off a single, full aperture, 1053nm (1ω) beamline before the beam propagates to the target chamber and directing it to a suite of precision laser diagnostics. It was instrumental in validating the performance of the final optics 3Ω frequency conversion system design when NIF was built. The PDS has recently been recommissioned after more than a decade of non-use and enhanced to better understand laser performance limitations1 and to characterize underperforming beams. In addition to recommissioning existing diagnostics for calorimetry, power, wavefront, near-field and far-field imaging, new diagnostics have been added: two types of time-resolved near field imaging systems; higher resolution wavefront imaging; and a 1ω spectrometer. Additionally, the beam transport system was upgraded to allow PDS to select among four different 1ω beamlines to enable improved understanding of beam-to-beam variations. Two of these four beams are top-hemisphere beams, while two are bottom-hemisphere, with known performance variations. The results from NIF Shots with the new and recommissioned PDS diagnostic (spatial resolution, dynamic range, time gating, etc..) will be reviewed and data up to 14 kJ, 3.2 TW will be presented.

A. D. Handler, S. J. Cohen, M. A. Erickson, T. E. Lanier, M. E. Ordoñez, N. S. Gottesman, J. M. Di Nicola, J. A. Folta, S. Yang, P. Wegner

Stark broadening measurements of Al II, Al III and He I 388.86nm spectral lines at high electron densities

Abstract: Experimental Stark width broadening parameters (w) for 5 spectral lines of singly (Al II) and 8 spectral lines of doubly ionized aluminum atoms (Al III) are presented. The for Al III values are the first experimental data. The experiment was conducted in laser-induced plasma in helium‑hydrogen gas mixture at reduced pressure. The laterally resolved spectra are recorded side-on. The plasma parameters are inferred after applying inverse Abel transform. The electron densities ranging from (0.98–4.86)×1023 m−3 are estimated relying on broadening of hydrogen Hβ spectral line. The electron temperature in experiment was in the range 20 000 K to 28 000 K and it was determined applying Boltzmann and Saha-Boltzmann method. Stark broadening parameters for Al II and Al III spectral lines are compared with available experimental and theoretical results. We also present experimental Stark widths and shifts (d) for neutral helium 388.86 nm spectral line at electron densities above 1×1023 m−3, where the existing number of w and d data is limited. Some of new Al III w values are convenient for plasma diagnostics.

Dejan Dojić, Miloš Skočić, Srdjan Bukvić, Stevan Djeniže

Dielectric barrier discharges applied for optical spectrometry

Abstract: The present review reflects the importance of dielectric barrier discharges for optical spectrometric detection in analytical chemistry. In contrast to usual discharges with a direct current the electrodes are separated by at least one dielectric barrier. There are two main features of the dielectric barrier discharges: they can serve as dissociation and excitation devices as well as ionization sources, respectively. This article portrays various application fields of dielectric barrier discharges in analytical chemistry used for elemental and molecular detection with optical spectrometry.

S.Brandt A.Schütz F.D. Klute J. Kratzer J. Franzke

Spectral characterization and white light generation by yttrium silicate nanopowders undoped and doped with Ytterbium(III) at different concentrations when excited by a laser diode at 975 nm

Abstract: We have studied nanophosphors of yttrium silicate (YSO) undoped and doped with different concentration of ytterbium (Yb3+) synthesized by using the sol-gel method. Structural and luminescence properties of the nanophosphors were studied experimentally by using different analytical techniques. For the structural analysis, we performed X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectrometry (EDS) measurements. Upconversion (UC) and the white light (WL) emission properties were investigated by using the near infrared cw laser excitation of 975 nm. The spectral properties have been found to depend on several physical parameters.

Hatun Cinkaya, Gonul Eryurek, Gokhan Bilir, John Collins, Baldassare Di Bartolo