Showing papers on "Doppler broadening published in 2005"

The XMM-Newton view of Mrk 3 and IXO 30

Abstract: We present the analysis of the XMM-Newton EPIC pn spectrum of the Seyfert 2 galaxy, Mrk 3. We confirm that the source is dominated by a pure Compton reflection component and an iron Kα line, both produced as reflection from a Compton-thick torus, likely responsible also for the large column density (1.36 +0.03 0.04 × 10 24 cm 2 ) which is pierced by the primary powerlaw only at high energies. A low inclination angle and an iron underabundance of a factor ≃ 0.82, suggested by the amount of reflection and the depth of the iron edge, are consistent with the iron Kα line EW with respect to the Compton reflection component, being 610 +30 50 eV. Moreover, the iron line width, σ = 32 +13 14 eV, if interpreted in terms of Doppler broadening due to the Keplerian rotation of the torus, puts an estimate to the inner radius of the latter, r = 0.6 +1.3 0.3 sin 2 i pc. Finally, two different photoionised reflectors are needed to take into account a large number of soft X-ray emission lines from N, O, Ne, Mg, Si, Fe L and the Fe xxv emission line at 6.71 +0.03

The XMM-Newton view of Mrk3 and IXO30

Abstract: We present the analysis of the XMM-Newton EPIC pn spectrum of the Seyfert 2 galaxy, Mrk3. We confirm that the source is dominated by a pure Compton reflection component and an iron K$\alpha$ line, both produced as reflection from a Compton-thick torus, likely responsible also for the large column density which is pierced by the primary powerlaw only at high energies. A low inclination angle and an iron underabundance, suggested by the amount of reflection and the depth of the iron edge, are consistent with the iron K$\alpha$ line EW with respect to the Compton reflection component. Moreover, the iron line width, if interpreted in terms of Doppler broadening due to the Keplerian rotation of the torus, puts an estimate to the inner radius of the latter, $r=0.6^{+1.3}_{-0.3} \sin^2{i}$ pc. Finally, two different photoionised reflectors are needed to take into account a large number of soft X-ray emission lines from N, O, Ne, Mg, Si, Fe L and the FeXXV emission line. RGS spectra show that the soft X-ray spectrum is dominated by emission lines, while the underlying continuum is best fitted by an unabsorbed powerlaw with the same photon index of the primary continuum, produced as reflection by a photoionised material with a column density of a few $10^{22}$ cm$^{-2}$. We also present the first X-ray spectrum of ROSAT source IXO30, which shows a huge iron line and is well represented either by an absorbed powerlaw or bremsstrahlung emission. Its spectral properties point to a likely identification in terms of a weak Galactic Cataclysmic Variable, but the lack of any optical counterpart precludes excluding other possibilities, like an ULX at the distance of Mrk3.

Nonlinear-Optic Silicon-Nanowire Waveguides

Abstract: Using a 4-mm-long compact silicon-nanowire waveguide, we demonstrated nonlinear-optic effects such as the spectral broadening of optical short pulses due to self-phase modulation and nonlinear transmittance due to two-photon absorption. At a 12 W input power level, we observed a 1.5-π nonlinear phase shift and a strong saturation of optical output power in a sample. We also estimated the third-order nonlinear coefficient n2 and the two-photon absorption coefficient β, and compared them with those previously reported.

Spectral broadening and diffusion by torsional motion in biphenyl

Abstract: We have studied biphenyl by time-dependent density-functional theory. In particular, we have analyzed the dependence of singlet excitation energies and transition dipoles on the torsional angle between the phenyl groups. The torsional spectrum has been computed quantum mechanically as well as semiclassically in order to understand how this influences the broadening of absorption and luminescence spectra. Our results are in best agreement with supersonic jet spectroscopy data, but also fit astonishingly well to spectra of biphenyl in condensed phase. Furthermore, we compare the torsional and vibrational relaxation and discuss qualitatively the general consequences for poly-para-phenylenes and related conjugated polymers as poly-thiophenes, considering, in particular, how side chains and solvents may affect the optical spectra.

Optimal spectral broadening in hollow-fiber compressor systems

Abstract: Supercontinuum generation in gas-filled hollow fibers is investigated using numerical simulation of the nonlinear propagation of light pulses in hollow waveguides. The use of the cascading hollow-fiber configuration allows one to significantly enhance the achievable spectral broadening, particularly in the high energy regime. General design criteria for a single- and a double-fiber configuration are presented, which allow the generation of high-energy supercontinua.

Route to broadband blue-light generation in microstructured fibers.

Abstract: We explore theoretically the possibility of generating broadband blue light by copropagating a short soliton pump pulse and a broader signal pulse in a microstructured fiber with a zero-dispersion wavelength located between the center wavelength of the pump and the signal pulses. We show that the unique properties of microstructured fibers should allow for broadening of the signal pulse’s spectrum by as much as a factor of 50 through the conjugate action of cross-phase modulation and a soliton self-frequency shift. The physical mechanism that leads to this large spectral broadening is analyzed by use of an extended nonlinear Schrodinger equation.

Excessive balmer line broadening in a plane cathode abnormal glow discharge in hydrogen

Abstract: Results of a Doppler spectroscopy study of the hydrogen Balmer alpha line in an abnormal glow discharge operated in pure hydrogen are reported. Measurements of line shapes are performed side-on to the discharge axis in a low electric field region of negative glow. The excessive Balmer alpha broadening is detected and its presence and linewidth is related to the collisions of fast hydrogen atoms with molecular hydrogen. The collision model enabled also an estimation of effective cross section data from the Balmer alpha axial intensity decay curves. Large excessive Balmer alpha line broadening in pure hydrogen and its dependence upon the direction of observation with respect to the electric field is in contradiction to the resonance transfer model, proposed byMills et al. in several publications [see, e.g., IEEE Trans. Plasma Sci. 31, 338 (2003)].

Positron localization effects on the Doppler broadening of the annihilation line: aluminum as a case study.

Abstract: Powered by TCPDF (www.tcpdf.org) This material is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. Calloni, A.; Dupasquier, A.; Ferragut, R.; Folegati, P.; Iglesias, M.M.; Makkonen, I.; Puska, M.J. Positron localization effects on the Doppler broadening of the annihilation line: aluminum as a case study

Line strengths and transition dipole moment of the ν2 fundamental band of the methyl radical

Abstract: The line strengths of nine Q-branch lines in the ν2 fundamental band of the methyl radical in its ground electronic state have been measured by diode laser absorption spectroscopy. The vibration–rotation spectrum of methyl was recorded in a microwave discharge in ditertiary butyl peroxide heavily diluted in argon. The absolute concentration of the radical was determined by measuring its kinetic decay when the discharge was extinguished. The translational, rotational, and vibrational temperatures, also required to relate the line strengths to the transition dipole moment, were determined from relative integrated line intensities and from the Doppler widths of the lines after allowing for instrumental factors. The line strengths of the nine Q-branch lines were used to derive a more accurate value of the transition dipole moment of this band, μ2=0.215(25) D. Improved accuracy over earlier measurements of μ2 (derived from line strengths of single lines) was obtained by integrating over the complete line profi...

Nonlinear-refractive-index measurement in As2S3 channel waveguides by asymmetric self-phase modulation

Abstract: The nonlinear refractive index (n2) of an As2S3 channel waveguide at 1.55 µm has been measured. The n2 was deduced when the spectral broadening and modulation due to self-phase modulation (SPM) were characterized. Owing to the temporal asymmetry of the injected pulse, a specific approach to asymmetric SPM is presented. The measurements have been performed for both photodarkened and nonphotodarkened etched thin films so that the effect of photodarkening on the n2 could be assessed.

Radiation trapping in a cold atomic gas

Abstract: We experimentally study radiation trapping of near-resonant light in a cloud of laser-cooled rubidium atoms. Unlike in most previous studies, dealing with hot vapors, collisional broadening is here negligible and Doppler broadening due to the residual atomic velocity is narrower than the homogeneous broadening. This is an interesting new regime, at the boundary between coherent and incoherent radiation transport. We analyze in detail our low-temperature data (quasi-elastic regime) and then provide some experimental evidence for Doppler-based frequency redistribution. The data are compared with an analytical model valid for coherent transport and a Monte Carlo simulation including the Doppler effect.

Excessive hydrogen and deuterium Balmer lines broadening in a hollow cathode glow discharges

Abstract: Results of a Doppler spectroscopy study of hydrogen and deuterium Balmer lines in the stainless steel and copper hollow cathode glow discharge, operated in pure hydrogen, deuterium and mixtures of inert gases with hydrogen, are reported. For all gases and gas mixtures plasma observations perpendicular to electric field revealed the excessively large Doppler broadening. By changing mode of glow discharge operation, the Doppler broadened line profiles in helium-hydrogen mixture are recorded parallel to the discharge electric field as well. The excessively broadened part of the Hα line profile is shifted towards blue or red wavelength by changing the direction of electric field vector. The presence of large excessive Balmer lines broadening in pure hydrogen and in its gas mixture with neon as well as shifting of the excessively broadened part of line profile by means of electric field is in contradiction with the resonance transfer model proposed by Mills et al. in several publications, see e.g. [IEEE Trans. Plasma Sci. 31, 338 (2003)].

Enthalpy Measurement in Inductively Heated Plasma Generator Flow by Laser Absorption Spectroscopy

Abstract: Laser absorption spectroscopy was applied for diagnostics of inductively heated plasma generator flows. Temporal variation of translational temperature was deduced from measured absorption line broadening because the flow properties fluctuated at 300 Hz in synchronization with the induction current. The specific total enthalpy and mole fraction of oxygen were estimated from the deduced temperature assuming thermochemical equilibrium. Consequently, the averaged degree of dissociation of oxygen is 0.92. The specific total enthalpy was estimated at 33.7 ± 2.9 MJ/kg; 39% of it was in the form of chemical potential. The results show good agreement with intrusive measurements.

Nonresonant dielectric hole burning in neat and binary organic glass formers.

Abstract: Binary mixtures of the molecular glass former 2-picoline in oligostyrene, in which the dielectric response of 2-picoline exhibits a particularly broad distribution of correlation times, are investigated by nonresonant dielectric hole-burning (NDHB) spectroscopy and the results are compared with NDHB in neat systems, in particular, glycerol. It turns out that in both substance classes spectral selectivity is achieved, which indicates that dynamics is heterogeneous, i.e., slow and fast responses coexist in the material. However, in binary systems the position of the spectral modifications is completely determined by the spectral density of the pump field, and thus shifts linearly with burn frequency as expected, also at pump frequencies around the alpha-relaxation maximum. It is shown that in binary systems the lifetime tau(rec) of the spectral modifications is determined by the burn frequency omega(p) and exceeds its inverse by about one order of magnitude, indicating long-lived dynamic heterogeneity. The data are described in terms of a previously suggested model of dynamically selective heating, which was extended to include intrinsic nonexponential relaxation. It turns out that the spectral broadening in binary mixtures is not only due to pronounced dynamic heterogeneity, but partially also due to intrinsic broadening of the relaxation function.

Spectral broadening of femtosecond pulses in a single-mode As-S glass fiber.

Abstract: We report a strong spectral broadening of femtosecond pulses propagating in a single-mode As-S glass fiber of 1.5 m length. The pump pulse spectrum is broadened by a factor of five when the input power is grown up to 16.4 mW. The broadened spectra are nearly symmetric and self-phase modulation is believed to be the dominant nonlinear effect responsible for this process.

Spatial distribution of the velocity distribution function of Fe atoms in a magnetron sputtering plasma source

Abstract: We examined the spatial distribution of the velocity distribution function of Fe atoms in a conventional dc magnetron sputtering source by laser-induced fluorescence (LIF) imaging spectroscopy. By measuring the Doppler broadening of the excitation spectrum of LIF, we evaluated the velocity distribution function of Fe at many positions in the discharge space. By calculating the first- and second-order moments of the velocity distribution function, we obtained two-dimensional maps of the average velocity and the effective temperature in the r-z plane of the cylindrically symmetric magnetron discharge. The map of the average velocity clearly indicates that Fe atoms have fast velocity in the region adjacent to the target at a low discharge pressure such as 3 mTorr, while at a high gas pressure such as 20 mTorr, the average velocity of Fe atoms is almost zero in the entire discharge space. On the other hand, it has been found from the map of the effective temperature that the velocity distribution function obs...

Real-time numerical simulation of Doppler ultrasound in the presence of nonaxial flow.

Abstract: Numerical simulations of Doppler ultrasound (DUS) relying on computational fluid dynamics (CFD) models of nonaxial flow have traditionally employed detailed (but computationally intensive) models of the DUS physics, or have sacrificed much of the physics in the interest of computational or conceptual simplicity. In this paper, we present a compromise between these extremes, with the objective of simulating the essential characteristics of DUS spectrograms in a real-time manner. Specifically, a precomputed pulsatile CFD velocity field is interrogated at some number, N, of discrete points distributed spatially within a sample volume of prescribed geometry and power distribution and temporally within a prescribed sampling window. Intrinsic spectral broadening is accounted for by convolving each of the point velocities with a semiempirical broadening function. Real-time performance is facilitated through the use of an efficient algorithm for interpolating the unstructured CFD data. A spherical sample volume with Gaussian power distribution, N = 1000 sampling points, and quadratic broadening function are shown to be adequate for simulating, at frame rates of 86 Hz on a 1.5 GHz desktop workstation, realistic-looking spectrograms at representative locations within a stenosed carotid bifurcation model. Via qualitative comparisons with matched in vitro data, these simulated spectrograms are shown to mimic the distinctive spectral envelopes, broadening and power characteristics associated with common carotid, stenotic jet and poststenotic recirculating flows. We conclude that the complex interaction between Doppler ultrasound and complicated clinically relevant blood flow dynamics can be simulated in real time via this relatively straightforward semiempirical approach.

Photochemistry of formaldehyde under tropospheric conditions.

Abstract: We report new results on the absorption cross sections and photochemical quantum yields for radical (H + HCO) production from formaldehyde in the wavelength interval from 308–320 nm, obtained at resolutions of better than 0.1 nm. The absorption cross sections, measured at resolutions close to the limit for Doppler broadening of HCHO, show rotationally resolved fine structure, with maximum values higher than those obtained in previous, lower resolution, studies. In this wavelength region, absorption cross sections peak at 2.3 × 10−19 cm2 molecule−1, but band-integrated values are in excellent accord with previous measurements. HCO absorption coefficients, measured by cavity ring-down spectroscopy following UV photolysis of HCHO at wavelengths across the 210510, 220430 and 230410 bands of the A1A2–1A1 transition, generally mimic the parent absorption band profiles. Division of these absorption coefficients by the high resolution parent absorption cross sections gives relative quantum yields for the H + HCO radical product channel that can be put on an absolute scale using single-wavelength literature values. These quantum yields are observed to show some variation with parent excitation wavelength (and thus with excited vibronic level). Addition of 200 Torr of N2 increases the HCO quantum yields.

Optimal spectral broadening in hollow-fiber compressor systems

Abstract: Supercontinuum generation in gas-filled hollow fibers is investigated using numerical simulation of the nonlin- ear propagation of light pulses in hollow waveguides. The use of the cascading hollow-fiber configuration allows one to signifi- cantly enhance the achievable spectral broadening, particularly in the high energy regime. General design criteria for a single- and a double-fiber configuration are presented, which allow the generation of high-energy supercontinua. characteristics (i.e., gas type and pressure, fiber length and ra- dius), in order to maximize the spectral broadening of light pulses, with a given energy and duration. Spectral broadening induced by self-phase-modulation (SPM) in gas-filled hollow fibers can lead to the generation of high-energy supercon- tinua, covering more than two octaves, thus offering the pos- sibility to generate pulses with a transform-limited duration below 2f s. This requires the development of ultrabroadband dispersive delay lines. Moreover, compression of selected portions of the supercontinuum gives the possibility to gener- ate sub-ten-fs pulses, tunable from the ultraviolet to the near- infrared (16). Using numerical simulations of the nonlinear propagation of a light pulse in a gas-filled fiber, we have deter- mined the limits, in terms of spectral broadening, of a single and a double stage hollow-fiber compressor. We show that a simple analytical model, which describes the evolution of a Gaussian pulse in a Kerr medium, allows one to calculate the spectral broadening factor in very good agreement with the re- sults of the numerical simulations. The paper is organized as follows: in Sect. 2 we briefly discuss the nonlinear equation, which will be used in the numerical simulation of the propa- gation of light pulses in hollow fibers. A simple analytical model, which describes the spectral broadening of Gaussian pulses in a Kerr medium, will be mentioned. In Sect. 3, gen- eral design criteria for the optimization of spectral broadening will be discussed, in the case of a single and a double fiber configuration. Finally Sect. 4 contains the conclusions. 2 Non-linear propagation in gas-filled hollow fiber

Remote determination of sample temperature by neutron resonance spectroscopy.

Abstract: The Doppler broadening of the lower energy neutron absorption resonances of natural hafnium, tantalum, iridium and rhenium have been studied for the purpose of measuring temperature in remote or isolated environments. Three methods for the determination of sample temperature from neutron transmission data were studied and a critical comparison of the efficacy of each method made. Fitting the observed resonance line shapes with analytical expressions incorporating instrument resolution and resonance parameters provided the most accurate measure of sample temperature with an estimated uncertainty of ± 10 ∘ C at 1000 ∘ C and did not require prior calibration experiments to be performed.

Thermal emission and absorption of radiation in finite inverted-opal photonic crystals

Abstract: We study theoretically the optical properties of a finite inverted-opal photonic crystal. The light-matter interaction is strongly affected by the presence of the three-dimensional photonic crystal and the alterations of the light emission and absorption processes can be used to suppress or enhance the thermal emissivity and absorptivity of the dielectric structure. We investigate the influence of the absorption present in the system on the relevant band edge frequencies that control the optical response of the photonic crystal. Our study reveals that the absorption processes cause spectral broadening and shifting of the band edge optical resonances, and determine a strong reduction of the photonic band gap spectral range. Using the angular and spectral dependence of the band edge frequencies for stop bands along different directions, we argue that by matching the blackbody emission spectrum peak with a prescribed maximum of the absorption coefficient, it is possible to achieve an angle-sensitive enhancement of the thermal emission/absorption of radiation. This result opens a way to realize a frequency-sensitive and angle-sensitive photonic crystal absorbers/emitters.

Temperature measurement in a Paris-Edinburgh cell by neutron resonance spectroscopy

Abstract: Neutron resonance spectroscopy is demonstrated as a viable and reliable method for the determination of sample temperatures in high-pressure, high-temperature neutron diffraction studies at neutron spallation sources. The technique operates by characterizing the thermally induced Doppler broadening of neutron absorption resonances of heavy nuclei present within the sample assembly observed in transmission. Accuracies of ±10K have been readily achieved with data acquisition times of approximately 40 min. It is shown that the temperatures determined by this technique are independent of the sample pressure provided that the sample temperature is kept above the Debye temperature of the material whose resonances are being examined. A short list of candidate resonances for temperature measurement by neutron resonance spectroscopy is presented and suggestions volunteered for the combinations of elements most suitable for temperature measurement based on the experience of the authors.

Diode Laser-Induced Fluorescence of Xenon Ion Velocity Distributions

Abstract: Comparison of a deconvolved ion energy distribution taken in a 500 V ion beam with retarding potential analyzer data showed bulk ion energy agreement within 1%, but only qualified similarity between the distributions Grid misalignment during the LIF experiment may be responsible for the usually broad Doppler broadening As a result, we are presently unable to reliably validate our deconvolution method at 8347 nm

Development of accelerator-based γ-ray-induced positron annihilation spectroscopy technique

Abstract: Accelerator-based γ-ray-induced positron annihilation spectroscopy performs positron annihilation spectroscopy by utilizing MeV bremsstrahlung radiation generated from an accelerator (We have named the technique “accelerator-based γ-ray-induced PAS,” even though “bremsstrahlung” is more correct here than “γ rays”. The reason for that is to make the name of the technique more general, since PAS may be performed by utilizing MeV γ rays emitted from nuclei through the use of accelerators as described later in this article and as in the case of positron lifetime spectroscopy [F.A. Selim, D.P. Wells, and J.F. Harmon, Rev. Sci. Instrum. 76, 033905 (2005)].) instead of using positrons from radioactive sources or positron beams. MeV γ rays create positrons inside the materials by pair production. The induced positrons annihilate with the material electrons emitting a 511-keV annihilation radiation. Doppler broadening spectroscopy of the 511-keV radiation provides information about open-volume defects and plastic deformation in solids. The high penetration of MeV γ rays allows probing of defects at high depths in thick materials up to several centimeters, which is not possible with most of the current nondestructive techniques. In this article, a detailed description of the technique will be presented, including its benefits and limitations relative to the other nondestructive methods. Its application on the investigation of plastic deformation in thick steel alloys will be shown.

High-resolution absorption cross sections of formaldehyde at wavelengths from 313 to 320 nm.

Abstract: Absorption cross sections have been measured for the 220430 and 230410 vibrational bands of the A1A2–1A1 electronic transition of formaldehyde in the wavelength range 313–320 nm. Accurate values are of considerable importance for atmospheric monitoring and to understand the photochemistry of this compound. The 0.10 cm−1 FWHM wavenumber resolution of the experiments is determined by the bandwidth of the ultraviolet laser used, and is a factor of 10 or more higher than any previously reported data. The absorption cross section data are thus obtained at a spectrometer resolution close to the Doppler broadening limit at 294 K of 0.07 cm−1 FWHM, for isolated rotational lines, but lifetime broadening effects contribute a further ∼0.5 cm−1 of width. Our spectral resolution is thus higher than required to resolve the sharpest spectral features and, as a consequence, the cross sections peak at greater values than previous studies of these structured rovibronic bands conducted at much lower spectrometer resolutions. Previous data can be quantitatively reproduced by convolution of the newly obtained spectra with lower-resolution instrument functions. Pressure broadening of regions of the spectra in the presence of up to 500 Torr of N2 is examined and the effects on peak absorption cross sections are very small. The influence of reduced temperature on the spectrum is also explored through experimental measurements and spectral simulations.