Scientific publications by model:
Hα Emission as a feedback control sensor for reactive sputter deposition of nano-structured, diamond-like carbon coatings
C. Christopher Klepper, Eric P. Carlson, Robert C. Hazelton, Edward J. Yadlowsky, Bao Feng, Mahmoud A. Taher, and Harry M. Meyer, III
Abstract
This paper discusses the potential use of the hydrogen atomic line emission at 656.3 nm (Hα ) as an effective in-situ sensor for a closed-loop control system to improve the reproducibility of reactive sputter deposition of nano-structured, metal-containing, hydrogenated, diamond-like carbon (Me:DLC:H) coatings. The paper includes experimental results showing a good correlation between Hα emission in the process plasma and the formation of metal-carbide, an important component of these coatings. The first attempts at actual feedback-control of the process showed that this sensor can be effective, at least over the stage of the deposition when mostly carbides are formed in the coating. A spectrally resolved analysis of the Hα emission for the various stages of the deposition have shown that the emission profile is dominated by a “hot” component ( ~10–20 eV), which can be attributed to dissociative excitation of molecular hydrogen (H2). The molecular hydrogen is understood to evolve from the coating as a result of carbon incorporation from the reactive gas (C2H2) and is particularly sensitive to metal carbide formation in the film, when most of the hydrogen is released from the surface in molecular form.
IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 33, NO. 2, APRIL 2005
Resonance Raman study of the phonon spectra in superconducting Bi-2212 and Y-123
M. Rübhausenb , M.V. Kleina, D. Budelmannb, B. Schulzb, P. Guptasarmac, M.S. Williamsenc, R. Liangd, D.A. Bonnd and W.N. Hardyd
Abstract
We studied the variation of phonon spectra with incident photon energy Ei in two superconducting samples, optimally doped YBCO (Tc=93.6 K) and overdoped Bi-2212 (Tc=82 K). Our results highlight the layered nature of the cuprates. Especially the buffer layers that are thought to be responsible for the doping of the CuO2 planes show complex phonon spectra. In Bi-2212 we find an activation of up to 13 phonon modes for a resonance that allows transitions into the Bi–O layers at 3.8 eV. For Y-123 we find also an activation of phonon modes as well as a huge matrix element when transitions into the chains at around 4.1 eV are possible. We also investigate the variation of the line shape of the O(II)–O(III) mode as a function of incident photon energy.
Journal of Physics and Chemistry of Solids 2006, Volume 67, Issues 1-3, Pages 312-315
Fully reflective deep ultraviolet to near infrared spectrometer and entrance optics for resonance Raman spectroscopy
B. Schulz, J. Bäckström, D. Budelmann, R. Maeser, M. Rübhausen, M. V. Klein, E. Schoeffel, A. Mihill and S. Yoon
Abstract
We present the design and performance of a new triple-grating deep ultraviolet to near-infrared spectrometer. The system is fully achromatic due to the use of reflective optics. The minimization of image aberrations by using on- and off- axis parabolic mirrors as well as elliptical mirrors yields a strong stray light rejection with high resolution over a wavelength range between 165 and 1000 nm. The Raman signal is collected with a reflective entrance objective with a numerical aperture of 0.5, featuring a Cassegrain-type design. Resonance Raman studies on semiconductors and on correlated compounds, such as LaMnO3, highlight the performance of this instrument, and show diverse resonance effects between 1.96 and 5.4 eV
Review of scientific instruments
2005, Volume 76, no7, pp. 073107.1-073107.12
Orbital ordering in LaMnO3 investigated by resonance Raman spectroscopy
Krüger R, Schulz B, Naler S, Rauer R, Budelmann D, Bäckström J, Kim KH, Cheong SW, Perebeinos V, Rübhausen M.
Abstract
Orbital ordering leads to an unconventional excitation spectrum that we investigate by resonance Raman scattering using incident photon energies between 1.7 and 5.0 eV. We use spectral ellipsometry to determine the corresponding dielectric function. Our results show resonant behavior of the phonon Raman cross section when the laser frequency is close to the orbiton-excitation energy of 2 eV in LaMnO3. We show an excellent agreement between theoretical calculations based on the Franck-Condon mechanism activating multiphonon Raman scattering in first order of the electron-phonon coupling and the experimental data of phonons with different symmetries.
Physical Review Letters, vol. 92, Issue 9, id. 097203
Primary realization of a spectral irradiance scale employing monochromator-based cryogenic radiometry between 200 nm and 20 µm
E W M van der Ham, H C D Bos and C A Schrama
Abstract
Here we report on an alternative approach for making spectral irradiance measurements of radiation sources traceable, employing our monochromator-based absolute cryogenic radiometer (ACR) facility to its full extent. The method makes use of the continuously tunable absolute radiant flux emerging from the ACR facility to characterize and calibrate the spectral irradiance responsivity of a second adjacent double-monochromator system. This system will be part of a new facility at NMi-VSL, called SIR, that will be used to measure spectral irradiance distributions of radiation sources from the ultraviolet to the far infrared. Following this traceability route, a fully characterized high-temperature Planckian radiator is not needed. Proof-of-principle measurements in the visible part of the spectrum show very encouraging results. Although the new facility is under construction, the theoretical background and a schematic description will be presented in this paper.
2003 Metrologia 40 S177-S180
Picosecond relaxation of Ni-centers in II–VI semiconductors
R. Heitz, A. Hoffmann and I. Broser
Abstract
The internal relaxation processes of the 3d-center Ni2+ and the recombination of photogenerated holes with Ni+-centers are investigated by means of time resolved luminescence spectroscopy of the 3T1(P)-3T1(F) Ni2+ transition in ZnS, CdS, ZnSe and CdSe. Ultrafast recombination processes starting at the 3T1(P)-states with time constants down to 60 ps are observed. In addition to the detected dipole transitions, which are allowed by a strong admixture of p-like wavefunctions to the 3d-states of Ni2+, competing nonradiative recombination processes are important. Radiative and nonradiative transition rates are determined. The excitation processes of the 3T1(P)-3T1(F) luminescence are studied in cw and time resolved experiments. Free holes are trapped at Ni+-centers forming shallow effective mass-like states, trapping times of 30 ps in ZnS and 50 ps in CdS are observed. The subsequent intracenter relaxation to the luminescent 3T1(P)-state takes place within a few picoseconds by radiotionless cascade processes involving the 1T2(G)-state. After some nanoseconds the dynamical behaviour of the Ni2+-luminescence is determined by energy transfer processes between shallow donors and the Ni2+-centers. The investigations give evidence of strong electronic coupling of the Ni2+ (d-d)-transitions to the host
Optical Materials I 1992, 75-83
Picosecond energy transfer between excitons and defects in II-IV semiconductors
R.Heitz, C.Fricke, A.Hoffmann and I.Broser
Abstract
The luminescences of bound excitons in various II-IV semiconductors are studied by means of
time resolved spectroscopy at liquid helium temperatures. A general trend of increasing lifetimes
with increasing binding energies is in reasonable agreement with the theory of Rashba and
Gurgenishvili indicating a predominant radiative decay. It is shown that the investigation of the
dynamics of weakly bound excitons provides the possibility to determine parameters of the free
exciton. An effective exciton mass of 1.06m0 for ZnO and a free excitan oscillator strength of
0.0014 for ZnS are determined. The limits of the model in case of deeply bound excitons as well
as the nonradiative decay channels are discussed. The observed luminescence risetimes due to
the formation of bound exciton complexes after generation of free excitons are investigated.
Materials Science Forum Vol. 83-87 (1992) pp. 1241-1246
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Thermal Dependence of the Cr-to-Nd Energy Transfer in Lanthanum Lutetium Gallium Garnet
G. Ozen and B. Dibartolo
Abstract
Photoluminescence, excitation, and response to pulsed excitation measurements show the existence of the Cr3+-to-Nd3+ energy transfer in lanthanum lutetium gallium garnet with an efficiency eta = 0.59 at room temperature. The transfer occurs radiatively and nonradiatively, and both transfer rates are temperature dependent within 15-550 K. The nonradiative transfer rate, calculated as a function of temperature by using the lifetime data of the Cr3+ ion in the crystal, increases slowly with increasing temperature.
Applied Spectroscopy, Vol. 53, Issue 11, pp. 1454-1458
Red Antenna States of Photosystem I from Cyanobacteria Synechocystis PCC 6803 and Thermosynechococcus elongatus: Single-Complex Spectroscopy and Spectral Hole-Burning Study
Kerry J. Riley, Tőnu Reinot, Ryszard Jankowiak, Petra Fromme, and Valter Zazubovich
Abstract
Hole-burning and single photosynthetic complex spectroscopy were used to study the excitonic structure and excitation energy-transfer processes of cyanobacterial trimeric Photosystem I (PS I) complexes from Synechocystis PCC 6803 and Thermosynechococcus elongatus at low temperatures. It was shown that individual PS I complexes of Synechocystis PCC 6803 (which have two red antenna states, i.e., C706 and C714) reveal only a broad structureless fluorescence band with a maximum near 720 nm, indicating strong electron-phonon coupling for the lowest energy C714 red state. The absence of zero-phonon lines (ZPLs) belonging to the C706 red state in the emission spectra of individual PS I complexes from Synechocystis PCC 6803 suggests that the C706 and C714 red antenna states of Synechocystis PCC 6803 are connected by efficient energy transfer with a characteristic transfer time of 5 ps. This finding is in agreement with spectral hole-burning data obtained for bulk samples of Synechocystis PCC 6803. The importance of comparing the results of ensemble (spectral hole burning) and single-complex measurements was demonstrated. The presence of narrow ZPLs near 710 nm in addition to the broad fluorescence band at 730 nm in Thermosynechococcus elongatus (Jelezko et al. J. Phys. Chem. B 2000, 104, 8093-8096) has been confirmed. We also demonstrate that high-quality samples obtained by dissolving crystals of PS I of Thermosynechococcus elongatus exhibit stronger absorption in the red antenna region than any samples studied so far by us and other groups.
J. Phys. Chem. B, 2007, 111 (1), pp 286–292
Biophysical and Structural Analysis of a Novel Heme b Iron Ligation in the Flavocytochrome Cellobiose Dehydrogenase
Frederik A. J. Rotsaert, B. Martin Hallberg, Simon de Vries, Pierre Moenne-Loccoz, Christina Divne, V. Renganathan and Michael H. Gold
Abstract
The fungal extracellular flavocytochrome cellobiose dehydrogenase (CDH)
participates in lignocellulose degradation. The enzyme has a cytochrome domain
connected to a flavin-binding domain by a peptide linker. The cytochrome
domain contains a 6-coordinate low spin b-type heme with unusual iron
ligands and coordination geometry. Wild type CDH is only the second example of
a b-type heme with Met-His ligation, and it is the first example of a
Met-His ligation of heme b where the ligands are arranged in a nearly
perpendicular orientation. To investigate the ligation further,
Met65 was replaced with a histidine to create a
bis-histidyl ligated iron typical of b-type cytochromes. The
variant is expressed as a stable 90-kDa protein that retains the flavin domain
catalytic reactivity. However, the ability of the mutant to reduce external
one-electron acceptors such as cytochrome c is impaired.
Electrochemical measurements demonstrate a decrease in the redox midpoint
potential of the heme by 210 mV. In contrast to the wild type enzyme, the
ferric state of the protoheme displays a mixed low spin/high spin state at
room temperature and low spin character at 90 K, as determined by resonance
Raman spectroscopy. The wild type cytochrome does not bind CO, but the ferrous
state of the variant forms a CO complex, although the association rate is very
low. The crystal structure of the M65H cytochrome domain has been determined
at 1.9 Å resolution. The variant structure confirms a
bis-histidyl ligation but reveals unusual features. As for the wild
type enzyme, the ligands have a nearly perpendicular arrangement. Furthermore,
the iron is bound by imidazole Nδ1 and Nε2 nitrogen atoms, rather than the typical Nε2 /Nε2 coordination encountered in bis-histidyl ligated heme proteins. To our knowledge, this is the first example of a bis-histidyl Nδ1 /Nε2 -coordinated protoporphyrin IX iron.
Journal of Physics and Chemistry of Solids
Volume 67, Issues 1-3, January-March 2006, Pages 312-315
Peroxodiferric Intermediate of Stearoyl-Acyl Carrier Protein Δ9 Desaturase: Oxidase Reactivity during Single Turnover and Implications for the Mechanism of Desaturation
John A. Broadwater, Jingyuan Ai, Thomas M. Loehr,Joann Sanders-Loehr, and Brian G. Fox
Abstract
Combined optical and resonance Raman studies have revealed the formation of an O2-adduct upon exposure of 4e- chemically reduced stearoyl-acyl carrier protein Δ9 desaturase to stearoyl-ACP and 1 atm O2. The observed intermediate has a broad absorption band at 700 nm and is remarkably stable at room temperature (t1/2≈26 min). Resonance Raman studies using 16O2 gas reveal vibrational features of a bound peroxide [vs(Fe-O2), 442 cm-1; vas(Fe-O2), 490 cm-1; v(O-O), 898 cm-1] that undergo the expected mass-dependent shifts when prepared in 16O18O or 18O2. The appearance of two Fe-O2 vibrations, each having a single peak of intermediate frequency with 16O18O, proves that the peroxide is bound symmetrically between the two iron atoms in a µ-1,2 configuration. The same results have been obtained in the accompanying resonance Raman study of ribonucleotide reductase isoform W48F/D84E [P. Moënne-Loccoz, J. Baldwin, B. A. Ley, T. M. Loehr, and J. M. Bollinger, Jr. (1998) Biochemistry 37, 14659-14663], thus making it likely that other members of the class II diiron enzymes form related peroxodiferric intermediates. Study of the reactivity of peroxodiferric δ9D revealed that this intermediate underwent 2e- reduction leading to an oxidase reaction and recovery of the resting ferric homodimer. In contrast, biological reduction of the same enzyme preparations using ferredoxin reductase and [2Fe-2S] ferredoxin gave catalytic desaturation with a turnover number of 20-30 min-1. The profound difference in catalytic outcome for chemically and enzymatically reduced Δ9D suggests that redox-state dependent conformational changes cause partition of reactivity between desaturase and oxidase chemistries. The Δ9D oxidase reaction represents a new type of reactivity for the acyl-ACP desaturases and provides a two-step catalytic precedent for the “alternative oxidase” activity recently proposed for a membrane diiron enzyme in plants and trypanosomes.
Biochemistry, 1998, 37 (42), pp 14664–14671
The Ferroxidase Reaction of Ferritin Reveals a Diferric µ-1,2 Bridging Peroxide Intermediate in Common with Other O2-Activating Non-Heme Diiron Proteins
Pierre Moënne-Loccoz, Carsten Krebs, Kara Herlihy, Dale E. Edmondson, Elizabeth C. Theil, Boi Hanh Huynh, and Thomas M. Loehr
Abstract
Ferritins are ubiquitous proteins that concentrate, store, and detoxify intracellular iron through oxidation of Fe2+ (ferroxidation), followed by translocation and hydrolysis to form a large inorganic mineral core. A series of mutagenesis, kinetics, and spectroscopic studies of ferritin led to the proposal that the oxidation/translocation path involves a diiron protein site. Recent stopped-flow absorption and rapid freeze-quench Mössbauer studies have identified a single peroxodiferric species as the initial transient intermediate formed in recombinant frog M ferritin during rapid ferroxidation [Pereira, S. A., Small, W., Krebs, C., Tavares, P., Edmondson, D. E., Theil, E. C., and Huynh, B. H. (1998) Biochemistry 37, 9871-9876]. To further characterize this transient intermediate and to establish unambiguously the peroxodiferric assignment, rapid freeze-quenching was used to trap the initial intermediate for resonance Raman investigation. Discrete vibrational modes are observed for this intermediate, indicating a single chromophore in a homogeneous state, in agreement with the Mössbauer conclusions. The frequency at 851 cm-1 is assigned as v(O-O) of the bound peroxide, and the pair of frequencies at 485 and 499 cm-1 is attributed, respectively, to vs and vas of Fe-O2-Fe. Identification of the chromophore as a µ-1,2 bridged diferric peroxide is provided by the isotope sensitivity of these Raman bands. Similar peroxodiferric intermediates have been detected in a mutant of the R2 subunit of ribonucleotide reductase from Escherichia coli and chemically reduced Δ9 stearoyl-acyl carrier protein desaturase (Δ9D), but in contrast, the ferritin intermediate is trapped from the true reaction pathway of the native protein. Differences in the Raman signatures of these peroxide species are assigned to variations in Fe-O-O-Fe angles and may relate to whether the iron is retained in the catalytic center or released as an oxidized product.
Biochemistry, 1999, 38 (17), pp 5290–5295
Visible spectroscopy measurements in the PBFA II ion diode (invited)
J. Bailey, A. L. Carlson, R. L. Morrison and Y. Maron
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 spectrograph 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. Review of Scientific Instruments is copyrighted by The American Institute of Physics.
Rev. Sci. Instrum. 61, 3075 (1990); doi:10.1063/1.1141686
Biosynthesis of topa quinone cofactor in bacterial amine oxidases. Solvent origin of C-2 oxygen determined by Raman spectroscopy.
Nakamura N, Matsuzaki R, Choi YH, Tanizawa K, Sanders-Loehr J.
Abstract
Resonance Raman spectroscopy is an excellent technique for providing structural information on the 2,4, 5-trihydroxyphenylalanine quinone (TPQ) cofactor in copper-containing amine oxidases. This technique has been used to investigate the copper- and O2-dependent biosynthesis of the TPQ cofactor in phenylethylamine oxidase (PEAO) and histamine oxidase from Arthrobacter globiformis. Incubation of the holoenzyme in H218O causes frequency shifts at 1684(-26) cm-1 in PEAO and at 1679(-28) cm-1 in histamine oxidase, allowing this feature to be assigned to the C=O stretch of a single carbonyl group at the C-5 position. When apoprotein is reacted with Cu(II) and O2 in the presence of H218O, the resultant holoproteins show increased shifts of -3 to -6 cm-1 in a number of other vibrational modes, particularly at 411 and 1397 cm-1. Because these small shifts persist when the H218O-regenerated protein is back-exchanged into H216O, they can be assigned to oxygen isotope substitution at the C-2 postion. No isotope shifts are observed when apoprotein is regenerated with Cu(II) in the presence of 18O2. Thus, it is concluded that the C-2 oxygen atom of TPQ originates from H2O rather than O2. The isotope dependence of the 1397-cm-1 mode allows it to be assigned to the C-O moiety at the C-2 position, with its low frequency being indicative of only partial double bond character. Similar frequency shifts due to 18O at C-2 are observed in the resonance Raman spectra of H218O-regenerated PEAO after derivatization of the C-5 carbonyl with either p-nitrophenylhydrazine (-5 cm-1 at 480 cm-1) or methylamine (-5 cm-1 at 1301 cm-1). Taken together, these results indicate that the TPQ cofactor in the native enzyme has substantial electron delocalization between the C-2 and C-4 oxygens and that only the C-5 oxygen has predominantly C=O character.
J Biol Chem. 1996 Mar 1;271(9):4718-24.
Characterization of Manganese(II) Binding Site Mutants of Manganese Peroxidase
Katsuyuki Kishi, Margo Kusters-van Someren,‡ Mary B. Mayfield, Jie Sun, Thomas M. Loehr, and Michael H. Gold*
Abstract
A series of site-directed mutants, E35Q, E39Q, and E35Q-D179N, in the gene encoding manganese peroxidase isozyme 1 (mnp1) from Phanerochaete chrysosporium, was created by overlap extension, using the polymerase chain reaction. The mutant genes were expressed in P. chrysosporium during primary metabolic growth under the control of the glyceraldehyde-3-phosphate dehydrogenase promoter. The mutant manganese peroxidases (MnPs) were purified and characterized. The molecular masses of the mutant proteins, as well as UV-vis spectral features of their oxidized states, were very similar to those of the wild-type enzyme. Resonance Raman spectral results indicated that the heme environment of the mutant MnP proteins also was similar to that of the wild-type protein. Steady-state kinetic analyses of the E35Q and E39Q mutant MnPs yielded Km values for the substrate MnII that were ∼50-fold greater than the corresponding Km value for the wild-type enzyme. Likewise, the kcat values for MnII oxidation were ∼300-fold lower than that for wild-type MnP. With the E35Q-D179N double mutant, the Km value for MnII was ∼120-fold greater, and the kcat value was ∼1000-fold less than that for the wild-type MnP1. Transient-state kinetic analysis of the reduction of MnP compound II by MnII allowed the determination of the equilibrium dissociation constants (KD) and first-order rate constants for the mutant proteins. The KD values were approximately 100-fold higher for the single mutants and approximately 200-fold higher for the double mutant, as compared with the wild-type enzyme. The first-order rate constants for the single and double mutants were ∼200-fold and ∼4000-fold less, respectively, than that of the wild-type enzyme. In contrast, the Km values for H2O2 and the rates of compound I formation were similar for the mutant and wild-type MnPs. The second-order rate constants for p-cresol and ferrocyanide reduction of the mutant compounds II also were similar to those of the wild-type enzyme.
Biochemistry, 1996, 35 (27), pp 8986–8994
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Pu-239/Pu-240 isotope emission spectroscopy in a laser-induced plasma
Coleman A. Smitha,, Max A. Martinezb, D.Kirk Veirsb and David A. CremerscAbstract
Laser-induced breakdown spectroscopy (LIBS) has been applied for the determination of plutonium isotope ratios through direct observation of atomic emission from laser-induced plasmas at high resolution. The Pu-239/Pu-240 isotope shift of -0.355 cm-1 from the plutonium atomic line at 594.52202 nm (Blaise et al., The Atomic Spectrum of Plutonium, Argonne National Laboratory Report ANL-83-95, 1984) is clearly resolved in our plasma conditions. Atomic emission is dispersed through a 2-m spectrometer in double pass mode and collected on an electronically gated, intensified charge-coupled device (ICCD) camera. The integrated peak areas obtained from curve-fitting closely match the Pu-239/Pu-240 isotopic ratios obtained from standard methods of thermal ionization mass spectrometry and gamma spectrometry. The observed plutonium linewidths were 0.19 cm-1 (0.0067 nm). These linewidths are within the experimental error of the ideal instrument-limited linewidth, which is calculated to be 0.15 cm-1 (0.0052 nm) based upon the known modulation transfer function for the ICCD system. This linewidth should allow LIBS to be applicable for isotopic ratio measurements for all of the light actinides.
Spectrochimica Acta Part B: Atomic Spectroscopy Volume 57, Issue 5, 31 May 2002, Pages 929-937
320-channel dual phase lock-in optical spectrometer
P. S. Fodor, S. Rothenberger, and J. JevyAbstract
The development of a multiple-channel lock-in optical spectrometer (LIOS) is presented, which enables parallel phase-sensitive detection at the output of an optical spectrometer. The light intensity from a spectrally broad source is modulated at the reference frequency, and focused into a high-resolution imaging spectrometer. The height at which the light enters the spectrometer is controlled by an acousto-optic deflector, and the height information is preserved at the output focal plane. A two-dimensional InGaAs focal plane array collects light that has been dispersed in wavelength along the horizontal direction, and in time along the vertical direction. The data is demodulated using a high performance computer-based digital signal processor. This parallel approach greatly enhances (by more than 100x) the speed at which spectrally resolved lock-in data can be acquired. The noise performance of a working system optimized for the 1.3 µm wavelength range is analyzed using a laser diode light source. Time-resolved absorption traces are obtained for InAs quantum dots embedded in a GaAs matrix, and for dispersed films of PbSe nanocrystals.
Rev. Sci. Instrum. 76, 013103 (2005); doi:10.1063/1.1830013
Intensities and self-broadening coefficients of weak water vapor lines in the 720-nm region determined by intracavity laser absorption spectroscopy
SINGH K. and O'BRIEN J. J.Abstract
The time-resolved quasi-cw form of intracavity laser spectroscopy is used for the quantitative determination of absolute intensities and self-broadening coefficients of weak vibration-rotation lines of water that absorb in the region of the 720-nm band. The studies have been conducted using a 0.68-m-long intracavity absorption cell, and the data are analyzed both by directly fitting the absorption lineshape and by the curve of growth method. Values determined for some of the stronger lines are compared with the ones obtained in previous studies where multipass absorption cells and alternative instrumental techniques were employed. The comparisons show that the accuracy of the intracavity laser spectroscopy technique is comparable to that obtained by the use of other techniques
Journal of molecular spectroscopy 1994, vol. 167, no1, pp. 99-108 (19 ref.)
Intensity measurements of methane lines in the 727 nm band studied by intracavity laser spectroscopy at temperatures down to 77 K
Singh, Kuldip; O'Brien J. J.Abstract
A time-resolved, quasi-cw form of intracavity laser absorption spectroscopy has been used to measure intensities of vibration-rotation lines of methane in the 727 nm region. Temperatures of 77, 195 and 296 K are employed. A 0.68 meter long, low temperature absorption cell, enclosed inside the resonator cavity of a dye laser, has been used to obtain effective absorption pathlengths of 0.6-4.0 km. Intensities of several vibration-rotation methane lines obtained by directly fitting Voigt profiles to the absorption lines are reported for the first time for absorption in the 727 nm band.
Chemical Physics Letters (ISSN 0009-2614), vol. 229, no. 1-2, p. 29-34
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CsBr and CsI UV photocathodes: new results on quantum efficiency and aging
B. K. Singh, E. Shefer, A. Breskin, R. Chechik and N. AvrahamAbstract
We report on the photoemission properties of 300 Ĺ thick transmissive- and 5000 Ĺ thick reflective UV-sensitive CsBr photocathodes. Following post-evaporation heat treatment at 70°C the absolute quantum efficiency is 35% at 150 nm, with a red boundary cut-off at about 195 nm. Extensive aging studies of CsBr and CsI photocathodes, under high photon flux and under ion bombardment in gas avalanche multiplication mode, were carried out for the first time without exposure to air. The results are compared with the previously published data on CsI aging and the methodology of the aging tests is discussed in details.
Nuclear Instruments and Methods in Physics Research Section A, Volume 454, Issue 2-3, p. 364-378.
Generation of sub-30 fs ultraviolet pulses by Raman induced phase modulation in nitrogen
Noack, F.; Steinkellner, O.; Tzankov, P.; Ritze, H.-H.; Herrmann, J.; Kida, Y.Abstract
We demonstrate compression of ultrashort light pulses in the ultraviolet (UV) by impulsively excited molecular wave-packets in nitrogen filled in a 25 cm long hollow waveguide of 128 µm diameter. After compression with CaF2 prisms the pulse duration was determined by XFROG to be 23 fs with a time-bandwidth product of 0.50. The advantages of our technique are high efficiency and the possibility to use it also for pulses at wavelength shorter than 200 nm. The experimental observations are explained by a theoretical model.
Optics Express, vol. 13, Issue 7, p.2467
VUV fluorescence from selective high-order multiphoton excitation of N2
Coffee, Ryan N. and Gibson, George N.Abstract
Recent fluorescence studies suggest that ultrashort pulse laser excitation may be highly selective. Selective high-intensity laser excitation holds important consequences for the physics of multiphoton processes. To establish the extent of this selectivity, we performed a detailed comparative study of the vacuum ultraviolet fluorescence resulting from the interaction of N2 and Ar with high-intensity infrared ultrashort laser pulses. Both N2 and Ar reveal two classes of transitions, inner-valence ns←np and Rydberg np←n'l'. From their pressure dependence, we associate each transition with either plasma or direct laser excitation. Furthermore, we qualitatively confirm such associations with the time dependence of the fluorescence signal. Remarkably, only N2 presents evidence of direct laser excitation. This direct excitation produces ionic nitrogen fragments with inner-valence (2s) holes, two unidentified transitions, and one molecular transition, the N+2 :X 2∑+g←C 2∑+u . We discuss these results in the light of a recently proposed model for multiphoton excitation.
Physical Review A, vol. 69, Issue 5, id. 053407
Calibration of VUV spectrometer-detector system using synchrotron radiation
McPherson, A. ; Rouze, N. ; Westerveld, W.B. ; Risley, J.S.Abstract
A new technique and apparatus have been developed for the measurement of absolute electron impact photoemission cross sections in the 30--150-nm wavelength range. Synchrotron light is used as the primary intensity standard for the calibration of the detection efficiency of a vacuum ultraviolet (VUV) spectrometer-detector system. A multiadjustable manipulator was used to position precisely a Seya-Namioka-type spectrometer-detector system with respect to a narrow ray of synchrotron radiation. By scanning the beam of synchrotron radiation across the surface of the grating in the spectrometer, precise simulation of the geometry of the light source encountered in the electron impact photoemission mesurement was realized. Analysis of the results underscores the fact that for spectrometer calibrations in the VUV, the calibration procedure depends on the geometry of the experimental source. The simultaneous determination of the absolute apparatus response function of the spectrometer--detector system and the geometrical factors pertaining to the electron impact photoemission source allows photoemission cross sections in the VUV to be determined with unparalleled precision.
Applied Optics (ISSN 0003-6935), vol. 25, Jan. 15, 1986, p. 298-310.
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Real-Time Measurement of Combustion Generated Particles with Photofragmentation-Fluorescence
Damm, Christopher J.; Lucas, Donald; Sawyer, Robert F.; Koshland, Catherine P.Abstract
Excimer laser fragmentation-fluorescence spectroscopy (ELFFS) is a viable technique for real-time monitoring of carbonaceous particles in combustion exhausts. The exhaust from a single-cylinder two-stroke engine is diluted and diverted into the laser interrogation region, resulting in a particle concentration of approximately 1 × 107/cm3. Light from a 193 nm ArF laser photofragments the particles and then produces fluorescence from the atomic carbon fragments at 248 nm, CH fragments at 431 nm, and C2 fragments at 468 nm. The atomic carbon fluorescence signal is proportional to the number concentration of particles in the laser interrogation region. The 100-shot (1 s) detection limit for particles in the exhaust is 1 mg/m3, expressed as a mass concentration of particulate matter. Interferences from carbon monoxide and carbon dioxide are negligible. The relative fluorescence yield at 248 nm is four times greater from particles than from the gas phase hydrocarbons present in the exhaust. This high yield suggests that the gas phase hydrocarbon interference would not be problematic for measurements of diesel exhaust, where the ratio of particulate carbon to gas phase hydrocarbon is high.
Applied Spectroscopy, Volume 55, Issue 11, Pages 360A-370A and 1435-1572 (November 2001) , pp. 1478-1482(5)
Use of the vacuum ultraviolet spectral region for laser-induced breakdown spectroscopy-based Martian geology and exploration
RADZIEMSKI Leon ; CREMERS David A. ; BENELLI Katharine ; KHOO Cynthia ; HARRIS Ronny D. ;Abstract
Several elements important to planetary geology (e.g. Br, C, Cl, P, S) and the human exploration of Mars (e.g. toxic elements such as As) have strong emission lines in the purge and vacuum ultraviolet (VUV) spectral region (100-200 nm). This spectral region has not been extensively studied for space applications using geological samples. We studied emissions from the laser-induced breakdown spectroscopy (LIBS) plasma in this region using a sample chamber filled with 7 torr (930 Pa) of CO2 to simulate the Martian atmosphere. Pressures down to 0.02 torr were also used to evaluate the effect of the residual CO2 on the spectra and to begin investigating the use of VUV-LIBS for airless bodies such as asteroids and the Moon. Spectra were recorded using a 0.3-m vacuum spectrometer with an intensified CCD (ICCD) camera. The effects of time delay and laser energy on LIBS detection at reduced pressure were examined. The effect of ambient CO2 on the detection of C in soil was also evaluated. Lines useful for the spectrochemical analysis of As, Br, C, Cl, P, and S were determined and calibration curves were prepared for these elements. Although LIBS is being developed for stand-off analysis at many meters distance, the experiments reported here were aimed at in-situ (close-up) analysis.
Atomic spectroscopy (ISSN 0584-8547) 2005, vol. 60, no2, pp. 237-248
A far-ultraviolet contamination-irradiation facility for in situ reflectance measurements
Steven R. Meier, June L. Tveekrem and Ritva A. M. Keski-KuhaAbstract
In this article, a contamination-irradiation facility designed to measure contamination effects on far-ultraviolet optical surfaces is described. An innovative feature of the facility is the capability of depositing a contaminant, photopolymerizing the contaminant with far-ultraviolet light, and measuring the reflectance of the contaminated sample, all in situ. In addition to describing the facility, we present far-ultraviolet reflectance measurements for a contaminated mirror.
Review of scientific instruments (ISSN 0034-6748) 1998, vol. 69, no10, pp. 3642-3644
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High-pressure hollow cathode discharges
Karl H Schoenbach, Ahmed El-Habachi, Wenhui Shi and Marco CioccaAbstract
Reducing the diameter of the cathode hole in a plane anode - hollow cathode geometry to m has allowed us to generate direct current discharges in argon at atmospheric pressure. Up to pressure times cathode hole diameter (pD) values of approximately 5 Torr cm, and at sub-mA currents, glow discharges (predischarges) are observed with a shape which is determined by the vacuum electric field. In the same pD range, but at higher currents of up to approximately 4 mA, the discharges are of the hollow cathode discharge type. At pD values exceeding 5 Torr cm the predischarges turn into surface discharges along the mica spacer between the electrodes. At currents > 4 mA filamentary, pulsed discharges are observed. Qualitative information on the electron energy distribution in the microdischarges has been obtained by studying the VUV emission from ionized argon atoms and the argon excimer radiation at 130 nm. The results of the spectral measurements indicate the presence of a relatively large concentration of electrons with energies > 15 eV over the entire pressure range. The fact that the current - voltage characteristic of the microdischarges has a positive slope over much of the current range where excimer radiation is emitted indicates the possibility of forming arrays of these discharges and using them in flat panel excimer lamps.
1997 Plasma Sources Sci. Technol. 6 468-477
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Determination of the spectral radiance of deuterium lamps using the storage ring Bessy as a primary radiometric standard
Tegeler, ErichAbstract
The electron storage ring BESSY is a primary radiometric standard of spectral irradiance, which has been used for the calibration of deuterium lamps as radiometric transfer standards of spectral radiance in the wavelength range 115-350 nm. The radiometer used for these measurements is described in detail. For λ > 165 nm the uncertainty of the spectral radiance of the calibrated lamps is if > 3%.
Nuclear Instruments and Methods in Physics Research Section A, Volume 282, Issue 2-3, p. 706-713.
Diagnostics by laser-induced fluorescence in the vacuum ultraviolet of hydrogen molecules with high rovibrational excitation
Thomas Mosbach and H.F. DobeleAbstract
The population dynamics of molecular hydrogen in its electronic ground state is of particular interest for the understanding negative ion production. The favored process is dissociative attachment of low energy electrons to highly excited electronic ground state molecules. We report on in-situ measurements of the population of these states in a pulsed hydrogen plasma using LIF in the VUV. The measurements are taken after the fast interruption of the discharge current. In the current range investigated the population of the vibrational states is highly suprathermal, and the theoretically predicted plateu in the distribution is clearly observed.
Institut fur Laser und Plasmaphysik, Universitat GH-Essen, D-45117 Essen
Implementation of a normal incidence spectrometer on an electron beam ion trap
S. B. Utter, P. Beiersdorfer, J. R. Crespo López-Urrutia and E. TräbertAbstract
Spectroscopic instrumentation is one of the keys to the exploration of high-temperature plasmas. The electron beam ion trap EBIT can serve as a tool for precise studies of highly charged ions in the laboratory and can help in setting spectroscopic standards for plasma studies. Recent efforts have focused on investigating the EUV, vacuum ultraviolet VUV , and UV regimes. We present here the implementation of a 1 m normal incidence spectrometer for use on the Lawrence Livermore National Laboratory high-energy EBIT Super-EBIT for spectral analysis of line emission of highly charged ions. Using two different gratings, our study encompasses a wide range of wavelengths spanning the VUV through the visible. Examples of measurements of optical spectra from krypton and argon are given.
Review of scientific instruments 1999, vol. 70 (2), no1, pp. 288-291
Luminescence of Pr3+ in SrAl12O19: Observation of two photon luminescence in oxide lattice
A. M. Srivastava and W. W. BeersbAbstract
The observation of photon-cascade emission (PCE) in Pr3+ activated SrAl12O19 under vacuum ultraviolet excitation (VUV) is reported and discussed. In this host lattice, the lowest-energy component of the Pr3+ 4f5d excited configuration is located above the 1S0 state. The excitation of the Pr3+ 4f5d state by VUV photons results in radiative emission originating from the 1S0 level state. The subsequent radiative emission from the 1P0 state confirms the photon-cascade emission of Pr3+ activated SrAl12O19. To the best of our knowledge this is the first observation of PCE in an oxide matrix.
Journal of Luminescence Volume 71, Issue 4, May 1997, Pages 285-290
PtSi–n–Si Schottky-barrier photodetectors with stable spectral responsivity in the 120–250 nm spectral range
K. Solt, H. Melchior and U. Kroth, P. Kuschnerus, V. Persch, H. Rabus, M. Richter, and G. UlmAbstract
Front-illuminated PtSi–n–Si Schottky barrier photodiodes have been developed for the ultraviolet and vacuum ultraviolet spectral range. Their spectral responsivity was determined in the 120–500 nm spectral range by use of a cryogenic electrical substitution radiometer operated with spectrally dispersed synchrotron radiation. For wavelengths below 250 nm, the spectral responsivity is about 0.03 A/W, comparable to that of GaAsP Schottky photodiodes. Unlike the GaAsP diodes, the new PtSi–n–Si diodes have a spatially uniform response which is virtually stable after prolonged exposure to short wavelength radiation. Even after a radiant exposure of 150 mJ cm–2 at wavelength 120 nm, the relative reduction in spectral responsivity remains below 0.2%. Due to these features, this type of photodiode is a promising candidate for use as secondary detector standard in the ultraviolet and vacuum ultraviolet spectral ranges.
Applied physics letters 1996, vol. 69, no24, pp. 3662-3664
Photoelectric emission from negative-electron-affinity diamond (111) surfaces: Exciton breakup versus conduction-band emission
C. Bandis and B. B. PateAbstract
We have recently reported that bound electron-hole pairs (Mott-Wannier excitons) are the dominant source of photoelectron emission from specially prepared [‘‘as-polished’’ C(111)-(1×1):H] negative-electron-affinity diamond surfaces for near-band-gap excitation up to 0.5 eV above threshold [C. Bandis and B. B. Pate, Phys. Rev. Lett. 74, 777 (1995)]. It was found that photoexcited excitons transport to the surface, break up, and emit their electron. In this paper, we extend the study of exciton-derived emission to include partial yield (constant final-state) analysis as well as angular distribution measurements of the photoelectric emission. In addition, we find that exciton-derived emission does not always dominate. Photoelectric emission properties of the in situ ‘‘rehydrogenated’’ (111)-(1×1):H diamond surface are characteristically different than emission observed from the as-polished (111)-(1×1):H surface. The rehydrogenated surface has additional downward band bending as compared to the as-polished surface. In confirmation of the assignment of photoelectric yield to exciton breakup emission, we find a significant enhancement of the total electron yield when the downward band bending of the hydrogenated surface is increased. The functional form of the observed total electron yield demonstrates that, in contrast to the as-polished surface, conduction-band electrons are a significant component of the observed photoelectric yield from the in situ hydrogenated (111)-(1×1):H surface. Furthermore, electron emission characteristics of the rehydrogenated surface confirms our assignment of a Fan phonon-cascade mechanism for thermalization of excitons.
Surface science 1996, vol. 350, no1-3, pp. 315-321
Nanosecond time-resolved vacuum ultraviolet spectrometer for ion diode spectroscopy
T. Nash, D. Noack, and A. B. FilukAbstract
A 1-m normal incidence spectrometer has been modified for use as a diagnostic of ion diode plasmas. To improve instrumental sensitivity, an elliptical mirror images an anode surface plasma onto the entrance slit of an f/10 normal incidence spectrometer. The detector is a time-resolving copper iodide coated microchannel plate stripline framing camera with 60-µm resolution, limiting instrumental resolution to 1 Ĺ with a 600 l/mm grating in first order. Reflectivity of optics and photoelectron efficiency limit the spectral range from 400 to 2000 Ĺ. With a 600- l/mm grating the detector spans a 600-Ĺ range. Applications of the instrument may include ion source divergence measurements from Doppler broadening, electric field measurements from Stark splittings or shifts, electron temperature from mean ionization state, and magnetic field measurements on high-power Z pinches from Zeeman splitting.
Review of Scientific Instruments; Journal Volume: 64:9, Pages: 2493-2495
High-speed programmable detector system for plasma spectroscopy
H. H. Mai, J. M. Larsen, K. Dimoff and J. CastracaneAbstract
Special electronic scanning circuits have been built to increase the resolution time of an intensified photodiode array assembly used for detecting EUV emission. The system can operate at 1-MHz sampling rate to provide data readout on two parallel output lines. The scanning time of a 1000-element array can be reduced to 500 µs. The system is programmable and can function sequentially at three different frequencies within a single scan. The device is CAMAC compatible and operated remotely by computer. It has been used to record spatial as well as temporal development of EUV radiation from the TEXTOR tokamak plasma.
Review of Scientific Instruments, Volume 57, Issue 5, May 1986, pp.866-873
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McPherson's XUV grazing incidence spectrograph for plasma diagnostics and its calibration
K. Koláceka, J. Schmidta, V. Boháceka, M. Rípaa, P. Vrbaa, O. Frolovb, M. Tichýb, A. Jancárekc, M. Vrbovác, E. Skladnik-Sadowskad, M. Sadowskid, and J. BaranowskidAbstract
The calibration of a McPherson’s fully computer-controlled grazing-incidence spectrograph Model 248/310G (Rowland circle diameter ≈ 1 m) with a MCP/CCD detection system is described. As a DC source of the XUV radiation served the Vacuum UV Hollow Cathode Light Source (McPherson Model 629), which was delivered together with the spectrograph. We concentrated on the MCP-centre- as well as across-MCP-wavelength calibration (a more general theoretical relation than in [1] was found), MCP gain uniformity, and CCD binning linearity. No attention was paid to a resolution of the system, because it changes with the wavelengths and it is determined by properties of the detection system. In general, it is usually much worse than the resolution of the spectrograph itself.
German-Polish Conference on Plasma Diagnostics for Fusion and Applications, Greifswald, Germany, September 4-6, 2002, Paper A 02
Generation of Coherent Soft-X-Ray Radiation Extending Far Beyond the Titanium L Edge
Enikö Seres, József Seres, Ferenc Krausz, and Christian SpielmannAbstract
Coherent soft-x-ray radiation up to photon energies of 700 eV is obtained by focusing several-mJ, 10-fs near infrared laser pulses into a He gas jet. The observed nearly constant photon yield over several hundred eVs may be attributed to nonadiabatic self-phase matching, originating from a substantial ionization within a fraction of the optical cycle of the driving laser pulse.
Physical review letters 2004, vol. 92, no16, pp. 163002.1-163002.3
Power scaling of a z-pinch extreme ultraviolet source
MCGEOCH Malcolm W. ;Abstract
A xenon Z-pinch1,2 generating extreme ultraviolet radiation at the Mo-Si mirror wavelength of 13.5nm has been scaled to emit increased power at a higher repetition frequency. The 25mm long by 3.0mm (FWHM) diameter pinch produces 1.5W of EUV radiation (2.5% bandwidth) into an axial 0.1sr solid angle when operated at 100Hz (100J stored). The measured average pinch liner heat load at 100Hz is 37W cm-2, corresponding to an average internal wall temperature of 8(PC. Electrode and liner erosion is very slight after more than 106 pulses at 100Hz. Source cleanliness was demonstrated via a two-mirror simulation of a condenser in which throughput was unchanged during a 106 pulse run at 50Hz. Amplitude stability was 12% (3σ) and positional stability was less than 4% of source diameter (lo). 13.5nm output scaled linearly with repetition frequency to more than 150Hz (58J stored). The cost of ownership for this source is estimated to be no greater than for an excimer laser illuminator. A plan is outlined for continued development to >1kHz and usable power of 16W
Proceedings of SPIE, the International Society for Optical Engineering 2000, vol. 3997, pp. 861-866
2-D Light Diffraction from CCD and Intensified Reticon Multichannel Detectors Causes Spectrometer Stray Light Problems
Richard W. Bormett and Sanford A. AsherAbstract
After the shutdown of the BESSY I electron storage ring, PTB's two normal-incidence monochromator beamlines for the calibration of radiation sources and detectors in the wavelength range from 40 nm to 400 nm were transferred to PTB's new radiometry laboratory at BESSY II. In this paper, the beamlines and their properties are briefly described. First results for the calibration of secondary source standards and detector standards at BESSY II are shown and demonstrate the successful re-establishment of the measurement capabilities. In the ultraviolet, calibration of deuterium lamps was reproduced within 1% and of silicon trap photodetectors within 0.2%.
Applied Spectroscopy, Vol. 48, Issue 1, pp. 1-6
Source and detector calibration in the UV and VUV at BESSY II
M. Richter, J. Hollandt, U. Kroth, W. Paustian, H. Rabus, R. Thornagel and G. UlmAbstract
After the shutdown of the BESSY I electron storage ring, PTB's two normal-incidence monochromator beamlines for the calibration of radiation sources and detectors in the wavelength range from 40 nm to 400 nm were transferred to PTB's new radiometry laboratory at BESSY II. In this paper, the beamlines and their properties are briefly described. First results for the calibration of secondary source standards and detector standards at BESSY II are shown and demonstrate the successful re-establishment of the measurement capabilities. In the ultraviolet, calibration of deuterium lamps was reproduced within 1% and of silicon trap photodetectors within 0.2%.
2003 Metrologia 40 S107-S110
Influence of current prepulse on capillary-discharge extreme-ultraviolet laser
Tan, C. A. and Kwek, K. H.Abstract
In this paper the influence of the prepulse current on a capillary-discharge 46.9nm Ne-like Ar extreme-ultraviolet laser is reported. A current pulse with a typical RC shape (decay time of ∼30µs ) was used as a prepulse. Measurements indicate that when the filling pressure is low, the output can be improved by reducing the time delay between the application of the prepulse current and the onset of the main discharge current. For high pressure the reverse is true. This change is most significant for time delays between 2 and 4µs , and beyond these time delays, the effect is less significant. This effect is attributed to the changes in the capillary channel pressure and also to the absorption of the laser emission by the plasma plume ejected during the prepulse. Thus, apart from ensuring a minimal amount of prepulse current to prevent nonuniformity effects, the timing of the application of the prepulse current is also important.
Physical Review A, vol. 75, Issue 4, id. 043808
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A soft X-ray grating monochromator for undulator radiation
Reininger, R.; Saile, V.Abstract
One of the new insertion devices to be installed in the expansion of the DORIS storage ring consists of three undulators designed to cover with the first harmonic the photon energy range between 70 and 2000 eV. The concepts for a high-resolution and high-throughput monochromator that will take full advantage of this powerful new beam line are discussed. The final design is a modified SX-700 type monochromator in which the focusing elliptical mirror is replaced by a spherical one. The aberrations due to the new mirror are minimized by elongating the exit slit arm of the conventional SX-700. The ultimate resolution expected is 0.03 eV at 152 eV and 0.6 eV at 1086 eV with a photon flux up to 5 × 1011 photons/(s-100 mA) at the sample. The spot size at the sample position is less than 0.4 × 1.0 mm2.
Nuclear Instruments and Methods in Physics Research Section A, Volume 288, Issue 2-3, p. 343-348.
High-resolution EUV spectra of core-excited 2P, 2D0 and 2F states of doubly ionised boron
R Bruch, K T Chung, E Trabert, P H Heckmann, B Raith and H R MullerAbstract
EUV spectra of B III are investigated by means of high-resolution fast-ion spectroscopic measurements. For the first time the decay of several even parity (1s2pnp)2P and odd parity (1s2pnd)2D0 core-excited levels has been identified by theoretical calculations where relativistic and mass polarisation effects are considered. The fine-structure splittings of these states are also predicted. The experimental results of this work are used to determine team energies for the B III system. Finally a level scheme for a 6.226 nm laser is proposed.
1984 J. Phys. B: At. Mol. Phys. 17 333-344
Multichannel grazing-incidence spectrometer for plasma impurity diagnosis: SPRED
Fonck, R.J. ; Ramsey, A.T. ; Yelle, R.V.Abstract
A compact vacuum ultraviolet spectrometer system has been developed to provide time-resolved impurity spectra from tokamak plasmas. Two interchangeable abberation-corrected toroidal diffraction gratings with flat local fields provide simultaneous coverage over the ranges 100-1100 A or 160-1700 A. The detector is an intensified self-scanning photodiode array. Spectral resolution is 2 A with the higher dispersion grating. Minimum readout time for a full spectrum is 20 msec, but up to seven individual spectral lines can be measured with a 1-msec time resolution. The sensitivity of the system is comparable with that of a conventional grazing-incidence monochromator.
Applied Optics, Vol. 21, Issue 12, pp. 2115-2123
A vacuum ulra-voilet spectrometer (Double SPRED) for the observation of the JET divertor plasma
R.C. Wolf, K.D. Lawson, I. Coffey, R. Giannella, C.J. Hancock, N.C. Hawkes, L.D. Horton, G. Janeschitz, H. Jemmeson, A.C. Maas, C.F. Maggi and M. Di MaioAbstract
The SPRED spectrometer is a VUV survey instrument that has been successfully employed on a number of plasma machines. Its use of a holographic grating results in a flat focal field, enabling the best spectral resolution to be achieved over the whole extent of the detector. A double SPRED spectrometer having two fixed gratings and two independently controlled detectors has been installed on the JET machine for the observation of the divertor plasma. An additional improvement over previous SPRED designs is the extended wavelength coverage of the detectors. The experimental setup, including the spectrometer design, the VUV detectors, the alignment and control systems are described. The commissioning of the spectrometer on JET has allowed the performance of the instrument to be assessed, in particular its wavelength calibration, spectral resolution, and the effect of the integral shielding to nuclear radiation-induced noise. First results include a comparison with the spectral emission from the bulk plasma of the JET tokamak, observed with a single SPRED instrument, which emphasizes that the dominant emission from the divertor originates from low ionization stages or low Z-impurities such as carbon. Evidance has been found for the localization of the line emission from within the divertor chamber and some features of the divertor VUV radiation during high performance plasmas are described. Future applications are also discussed.
Control of high-order harmonic emission using attosecond pulse trains
J. Biegert; A. Heinrich; C. P. Hauri; W. Kornelis; P. Schlup; M. P. Anscombe; M. B. Gaarde; K. J. Schafer; U. KellerAbstract
We show that attosecond pulse trains are a natural tool to control strong field processes such as high-order harmonic generation. Coherently combining an attosecond pulse train with an IR driving field, we predict and experimentally confirm enhancement and spectral narrowing of the harmonic yield at photon energies around 90 eV. The use of an attosecond pulse train to seed the harmonic generation process replaces tunneling ionization with a single-photon ionization step, therefore permitting the manipulation of the time-frequency properties of high-order harmonic generation already at the single-atom level.
Journal of Modern Optics, Volume 53, Issue 1 & 2 January 2006 , pages 87 - 96
XUV SPECTROSCOPY IN JET
K. Behringer, B. Denne, G. Maygar, M. Mattoli, N.J. Peacock, J. Ramette, B. Saoutic and J.L. SchwobAbstract
The 2m extreme grazing incidence XW Schwob-Fraenkel spectrometer has been described in detail [1]. Its use on the TFR tokamak is presented in a parallel paper [2]. The instrument installed on JET differs in that it has two microchannel plates scanning independently two portions of the spectral range from 10 to 335Ĺ. A full scan takes 164 ms, due to the low number of photons. 127 spectra may be taken during a 20s tokamak discharge. The calculated and measured spectral resolution (FWHM) with a 600g/mm Bausch and Lomb grating and 20 µm entrance slit is shown in Fig. 1 for detector positions, y, between 200 and 390 mm (corresponding wavelengths of the central pixels are 85 and 310 Ĺ, respectively).
J. Phys. Colloques 49 (1988) C1-387-C1-390
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Advances in fiber-optic based UV resonance Raman spectroscopy techniques for anatomical and physiological investigations
SCHULZE H. G.; BARBOSA C. J.; GREEK L. S.; TURNER R. F. B.; HAYNES C. A.; KLEIN K.-F.; BLADES M. W.;Abstract
Ultraviolet resonance Raman spectroscopy (UVRRS) is becoming a very popular spectroscopic method for bioanalytical investigations due to its high sensitivity, lack of fluorescence, and suitability for use in aqueous solutions. We have made a number of technological advances, especially the development of fiber-optic-based technologies, which permit the performance of remote/in-situ UVRRS measurements. We will be reporting on improved optical fiber probes (OFPs) and demonstrate their benefits in performing UVRRS on neurotransmitters, saliva, and urine.
Biomedical applications of Raman spectroscopy. Conference, San Jose CA , ETATS-UNIS (25/01/1999) 1999, vol. 3608, pp. 157-166
Strong photoluminescence in ammonia plasma treated amorphous-SiC thin films deposited by laser ablation
S. Ghosh, P. Bhattacharya, and D. N. BoseAbstract
Amorphous-SiC films have been deposited by pulsed laser ablation on silicon substrates. Photoluminescence (PL) studies showed two broad bands with peaks at 1.34 and 1.72 eV for these unhydrogenated films. On NH3 passivation the intensity of the 1.34 eV peak increased by a large factor of 40–50 with full width at half-maximum (FWHM) decreasing to 13.5 meV at 12 K. The activation energy of this level was found to be 24 meV. These results are in contrast with those from unhydrogenated a-Si. A possible mechanism responsible for PL enhancement is discussed.
Applied physics letters 1996, vol. 68, no21, pp. 2979-2981
Advances with tungsten coil atomizers : Continuum source atomic absorption and emission spectrometry
RUST Jennifer A. ; NOBREGA Joaquim A. ; CALLOWAY Clifton P. ; JONES Bradley T. ;Abstract
Two new tungsten coil spectrometers are described: a continuum source tungsten coil atomic absorption spectrometer and a tungsten coil atomic emission spectrometer. Both devices use a 150 W tungsten coil extracted from a slide projector bulb. The power is provided by a computer-controlled, solid state, constant current 0-10 A supply. The heart of the optical system is a high-resolution spectrometer with a multi-channel detector. The continuum source system employs xenon or deuterium lamps, and is capable of multi-element analyses of complex samples like engine oil, urine, and polluted water. Spiked engine oil samples give mean percent recoveries of 98 ' 9, 104 ' 9, and 93 ' 0.8 for Al, V, and Ni, respectively. Copper, Zn, and Cd are determined in urine samples; while Cd, Co, Yb, and Sr are determined in water samples. Detection limits for Cd, Zn, Cu, Yb, Sr, and Co are: 8, 40, 1, 4, 1, and 4 µg 1-1 The technique of tungsten coil atomic emission spectrometry using a 150 W commercial projector bulb is reported for the first time. Calcium, Ba, and Sr are determined with detection limits of 0.01, 0.5, and 0.1 µg 1-1. Relative standard deviations are lower than 10% in each case, and Sr is determined in two water standard reference materials.
Atomic spectroscopy 2005, vol. 60, no5, pp. 589-598
Fast high resolution echelle spectroscopy of a laboratory plasma
Cothran, C. D.; Fung, J.; Brown, M. R.; Schaffer, M. J.Richard W. Bormett and Sanford A. AsherAbstract
An echelle diffraction grating and a multianode photomultiplier tube are paired to construct a high resolution (R=λ/δλ~2.5×104) spectrograph with fast time response for use from the UV through the visible. This instrument has analyzed the line shape of C III impurity ion emission at 229.687 nm over the lifetime (~100 µs) of the hydrogen plasmas produced at SSX. The ion temperature and line of sight average velocity are inferred from the observed thermal broadening and Doppler shift of the line. The time resolution of these measurements is about 1 µs, sufficient to observe the fastest magnetohydrodynamic activity.
Review of scientific instruments 2006, vol. 77, no6
Multichord spectroscopy of the DIII-D divertor region
N.H. BROOKS, A. HOWALD, K. KLEPPER, P. WESTAbstract
A multichannel spectrometer with high spectral resolution (0.01 nm) and high temporal resolution (0.5 msec) has been configured to collect data simultaneously from eight viewchords spanning the divertor region of DIII-D. Fiberoptically coupled to a wide-field lens with a vertical view of the vessel floor, the instrument will be capable of differentiating the behavior of impurity line emission at the inner and outer divertor strike points, on and off the Advanced Divertor Program (ADP) ring, on the face of the Divertor Material Exposure System (DIMES) probe, and in the region of the lower centerpost. Used with a coarse grating (300 grooves/mm), spectral coverage of each spatial channel is 15 nm with 0.3 nm resolution; used in high order with a 1200 groove/mm grating, the instrument is capable of resolving Doppler profiles. Spatial variation of gas recycling and impurity influx will be studied for both singleand double-null divertor configurations in low and high density operating regimes.
GENERAL ATOMICS PROJECT 3466, APRIL 1992
Dynamics of laser ablation plume penetration through low pressure background gases
David B. Geohegan, Alexander A. PuretzkyAbstract
The dynamics of laser-ablated yttrium plume propagation through background argon have been investigated with fast time- and spatially-resolved plasma diagnostics in order to characterize a general phenomenon believed to be important to film growth by pulsed laser deposition (PLD). During expansion into low-pressure background gases, the ion flux in the laser ablation plasma plume is observed to split into fast and slow components over a limited range of distances including those typically utilized for PLD. Optical absorption and emission spectroscopy are employed to simultaneously identify populations of both excited and ground states of Y and Y+ . These are correlated with intensified-CCD (ICCD) photographs of visible plume luminescence and ion fluxes recorded with fast ion probes. These measurements indicate that plume-splitting in background gases is consistent with scattering of target constituents by ambient gas atoms. The momentum transfer from these collisions produces a transition from the initial, ``vacuum'' velocity distribution into a velocity distribution which is significantly slowed in accordance with shock or drag propagation models.
Appl. Phys. Lett. 67, 197 (1995)
Fast high resolution echelle spectroscopy of a laboratory plasma
C.D. Cothran, J. Fung, M.R. Brown, M.J. SchafferAbstract
An echelle diffraction grating and a multianode photomultiplier tube are paired to construct a high resolution (R=λ/δλ≈2.5×104) spectrograph with fast time response for use from the UV through the visible. This instrument has analyzed the line shape of C III impurity ion emission at 229.687 nm over the lifetime (≈100 µs) of the hydrogen plasmas produced at SSX. The ion temperature and line of sight average velocity are inferred from the observed thermal broadening and Doppler shift of the line. The time resolution of these measurements is about 1 µs, sufficient to observe the fastest magnetohydrodynamic activity.
Rev. Sci. Instrum. 77, 063504 (2006)
Absolute calibration of a vacuum Czerny–Turner spectrometer in the range 1200–7000 Ĺ
L. Carraro, M. Cortiana, M. E. Puiatti, F. Sattin, P. Scarin, and M. ValisaAbstract
The vacuum Czerny–Turner high-resolution spectrometer observing the plasma of the reversed-field-pinch device RFX has been absolutely calibrated in the spectral range 1215–7000 Ĺ, in order to measure the emission spectrum in absolute units, with particular reference to the heliumlike carbon and oxygen ion lines. The source used to calibrate the spectrometer in the vacuum and near-ultraviolet region is a deuterium lamp; its spectral radiance was determined by comparison with the synchrotron radiation of the electron storage ring BESSY, in Berlin. A typical error of 35% has been estimated. In the visible a standard tungsten lamp has been used. The calibration has been transferred to an ultragrazing incidence XUV spectrometer by means of the branching-ratio technique, using the intensity ratio between the intercombination 1s2 1S–1s2p 3P0 and the 1s2s 3S–1s2p 3P0 transitions of carbon, nitrogen, and oxygen heliumlike ions.
Rev. Sci. Instrum. 66, 613 (1995)
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Rotational-resolved pulsed field ionization photoelectron bands for H2+(X 2Σg+, v+=0, 2, 9 and 11)
S. Stimsona, Y. -J. Chena, M. Evansa, C. -L. Liaoa, C. Y. Nga, C. -W. Hsub and P. HeimannbAbstract
We present here the assignment and simulation of rotational transitions for the H2+(X 2Σg+, v+, 2, 9 and 11) vibronic bands using the Buckingham–Orr–Sichel (BOS) model. The simulation shows that perturbation of PFI-PE rotational line intensities due to near-resonance autoionization decreases as v+ increases. Experimental rotational constants for H2+(X 2Σg+, v+, 2, 9 and 11) are determined with higher accuracy than those obtained in previous He I and Ne I photoelectron studies. In agreement with previous experimental and theoretical investigations, only the ΔN=0 and ±2 rotational branches are observed in the PFI-PE spectrum for H2.
Chemical Physics Letters Volume 289, Issues 5-6, 19 June 1998, Pages 507-515
A High Resolution Study of Low Lying Correlation Satellites in Xenon
R. C. Shiell, M. Evans1, S. Stimson1, C-W. Hsu2, C. Y. Ng1, and J. W. HepburnAbstract
The technique of pulsed field ionization–zero kinetic energy photoelectron spectroscopy, typically applied to the investigation of ionic states of atoms and molecules resulting from single electron excitation, has been used to probe the correlation satellite states of xenon between 23.6–24.7 eV. The resulting spectra show the formation of clearly resolved satellite states with intensities of a similar magnitude to that of the 5s5p6 2S1/2 ionic state. This technique can be extended to other atomic and molecular species to obtain the positions and cross sections for the formation of such states.
Physical review letters 1998, vol. 80, no3, pp. 472-475
High-Resolution Infrared-Vacuum Ultraviolet Photoion and Pulsed Field Ionization-Photoelectron Methods for Spectroscopic Studies of Neutrals and Cations
Xi Xing, Beth Reed, Mi Kyung Bahng, Peng Wang, Hin Koo Woo, Sun Jong Baek, Chee Shing Lam and Cheuk Yiu NgAbstract
We show that by scanning the frequency of a single mode infrared (IR) optical parametric oscillator (IR-OPO) laser to excite the molecular species of interest and fixing the frequency of a vacuum ultraviolet (VUV) laser to photoionize the IR excited species, high-resolution IR spectra of polyatomic neutrals can be obtained with high sensitivity. The fact that this IR-VUV-photoion (IR-VUV-PI) method is based on VUV photoionization probe, and thus, allows the identification of the neutral IR absorber, makes it applicable for IR spectroscopy measurements of isotopemers, radicals, and clusters, which usually exist as impure samples. The highly resolved IR-VUV-PI measurements achieved using the single mode IR-OPO laser have made possible the selection of single rovibrational states of CH3X (X = Br and I), C2H4, and C3H4 for VUV-pulsed field ionization-photoelectron (VUV-PFI-PE) measurements, resulting in rovibrationally resolved photoelectron spectra for these polyatomic molecules. These experiments show that the signal-to-noise ratios of the IR-VUV-PI and IR-VUV-PFI-PE spectra obtained by employing the high-resolution IR-OPO laser are significantly higher than those observed in previous IR-VUV-PI and IR-VUV-PFI-PE studies using a low-resolution IR-OPO laser. Further improvement in sensitivity of IR-VUV-PI and IR-VUV-PFI-PE measurements by using the collinear arrangement of IR-VUV lasers and molecular beam is discussed.
2008 Chin. J. Chem. Phys. 21 193-201
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