Showing papers on "Doppler broadening published in 1990"
TL;DR: In this article, visible spectroscopic measurements of the Doppler broadened spectral lines, resulting from charge exchange recombination interactions between beam neutral atoms and plasma ions, are performed to determine ion temperatures, and toroidal and poloidal rotation velocities.
Abstract: In DIII‐D, visible spectroscopic measurements of the He ii 468.6 nm and C vi 529.2 nm Doppler broadened spectral lines, resulting from charge exchange recombination interactions between beam neutral atoms and plasma ions, are performed to determine ion temperatures, and toroidal and poloidal rotation velocities. The diagnostics system comprises 32 viewing chords spanning a typical minor radius of 63 cm across the midplane, of which 16 spatial chords span 11 cm of the plasma edge just within the separatrix. A temporal resolution of 260 μs per time slice can be obtained as a result of using MCP phosphors with short decay times and fast camera readout electronics. Results from this system will be used in radial electric field comparisons with theory at the L–H transition and ion transport analysis.
100 citations
TL;DR: The model presented here gives the D-lines absorption coefficients of alkali-metal vapors in the presence of an arbitrary static magnetic field and experimental measurements of D-line absorption profiles show excellent agreement with theoretical predictions.
Abstract: When atoms are placed in a static magnetic field, they undergo shifts of their energy levels and changes in their transition probabilities. These two effects must be taken into account when considering absorption profiles of alkali-metal D lines, which result from the contribution of many transitions influenced by the laser spectrum and Doppler broadening. The model presented here gives the D-line absorption coefficients of alkali-metal vapors in the presence of an arbitrary static magneitc field. They are evaluated considering various laser polarizations. Experimental measurements of D-line absorption profiles for $^{85}\mathrm{Rb}$, $^{87}\mathrm{Rb}$, and $^{133}\mathrm{Cs}$ isotopes show excellent agreement with theoretical predictions.
100 citations
TL;DR: In this article, the authors identified injection-recombination shot noise in the tuning region as a significant linewidth broadening mechanism in wavelength-tunable laser diodes.
Abstract: Injection-recombination shot noise in the tuning region is identified as significant linewidth broadening mechanism in wavelength-tunable laser diodes. Depending on the tuning efficiency this power independent linewidth broadening is typically around 4–20 MHz. Useful formulas for the evaluation of this broadening and design rules for an improvement of the devices are given.
82 citations
TL;DR: In this paper, the authors measured the pressure broadening of the 31,3-22,0 transition of water over the 80 to 600 K temperature region for O2, N2, and He collision partners.
59 citations
TL;DR: In this article, the S3←S0 transition of CS2 in cyclohexane, pentane, acetonitrile, hexadecane, and perfluorohexane solvents has been measured.
Abstract: Electronic absorption spectra, resonance Raman spectra and quantum yields, and total emission yields have been measured for the S3←S0 transition of CS2 in cyclohexane, pentane, acetonitrile, hexadecane, and perfluorohexane solvents. The solution‐phase absorption spectra are significantly broadened and redshifted relative to the vapor. The solution‐phase S3 state lifetimes inferred from the total emission yields are 0.6–1.0 ps, close to the vapor‐phase lifetime, while the resonance Raman quantum yields imply electronic dephasing times of 25–50 fs in solution. This rapid dephasing due to intermolecular (solvent–solute) interactions is sufficient to account for almost all of the increased electronic spectral breadth in solution. The data are analyzed quantitatively with the aid of a stochastic theory of line broadening that accounts for solvent memory effects, and evidence is found for non‐Markovian (nonexponential in time) electronic dephasing. Possible physical origins for the rapid electronic dephasing in solution are suggested, and the relevance of these results to other dynamical processes in liquids such as activated barrier crossing and electron transfer reactions is discussed.
57 citations
TL;DR: In this article, a model of the lifetime broadening due to intraband Auger processes of the Landsberg type is described and developed for the case of electron-electron scattering in a 2D system.
Abstract: Experimental observations of spontaneous emission spectra from GaAs-AlGaAs quantum well lasers shown that spectral broadening should be included in any realistic model of laser performance. A model of the lifetime broadening due to intraband Auger processes of the Landsberg type is described and developed for the case of electron-electron scattering in a 2-D system. The model is applied to the calculation of gain and spontaneous emission spectra and gain-current relationships in short-wavelength GaAs-AlGaAs quantum well lasers, and the results are compared with those obtained using both a fixed intraband scattering time and one that varies as n/sup -1/2/, where n is the volume injected carrier density. >
50 citations
TL;DR: In this paper, the authors measured the spectral broadening due to an Er3+-doped fiber amplifier operating at 1.535µm and found the amount of broadening to be less than 20kHz for an amplifier operating with 17dB gain.
Abstract: Erbium-doped fibre amplifiers (EDFA) operating in the 1.5µm wavelength region will play an important role in future optical communication systems. Such devices offer large, polarisation-independent gain, low noise and high efficiency. Advanced coherent communication systems employing optical amplifiers in combination with phase or frequency modulation will allow for greatly increased system capacity and are therefore of considerable interest. However, coherent systems may suffer from spectral broadening due to phase noise introduced by the optical amplifiers and this may limit the number of amplifiers which can be concatenated in an optical link. To quantify the effect, we have measured for the first time spectral broadening due to an Er3+-doped fibre amplifier operating at 1.535µm, and have found the amount of broadening to be less than 20kHz for an amplifier operating with 17dB gain.
49 citations
TL;DR: In this paper, a five-spectrometer array has been designed to provide high-wavelength resolution x-ray spectra from the Alcator C-Mod plasma using von Hamos type spectrometers.
Abstract: A five‐spectrometer array has been designed to provide high‐wavelength resolution x‐ray spectra from the Alcator C‐Mod plasma Each independently scannable von Hamos type spectrometer consists of a variable entrance slit, quartz crystal, and position sensitive proportional counter, and has 3 cm spatial resolution with a resolving power of 4000 The wavelength range of each spectrometer is from 28 to 40 A, which covers the complete Rydberg series of helium‐ and hydrogen‐like argon Wavelengths are remotely selectable, with 120 mA covered at any one setting The array will provide single shot ion temperature profiles by measuring the Doppler broadening of the resonance lines of argon Five proportional counters have been fabricated and all five spectrometers have been constructed Calibration spectra using cadmium and scandium anode sources have been obtained, and measured performance characteristics are presented
45 citations
34 citations
04 Dec 1990
TL;DR: In this article, it was shown that the Doppler bandwidth remains unchanged even when one or more scatterers moving with constant velocity along an infinite straight line is shifted in the field without change of orientation.
Abstract: It is known that if single-frequency, continuous-wave ultrasound or electromagnetic energy is reflected from straight line flow, defined here as one or more scatterers moving with constant velocity along an infinite straight line, the Doppler effect will shift the echo spectrum center frequency from the transmitted value, and broaden its bandwidth. It is shown here that if such straight line flow is shifted anywhere in the field without change of orientation, the absolute echo bandwidth remains unchanged. This result is unexpected, since the bandwidth arises from amplitude modulation of the echo from the scatterers as they pass through the incident field, and the shape of this field varies with position. The Doppler bandwidth may therefore be used to estimate the transverse component of the flow velocity anywhere in the sound beam. The effect of the system relative aperture on the minimum spectral broadening and maximum frequency indication may also be assessed at any range. >
32 citations
TL;DR: In this paper, De 1 satellite radio observations were conducted in the 1525-5925 Hz range during a pass over an ionospheric heating facility; the waves were detected during a 2-min period, and the measurements indicated pulse-stretching by a few hundred msec, in conjunction with spectral broadening of about 10 Hz.
Abstract: DE 1 satellite radio observations were conducted in the 1525-5925 Hz range during a pass over an ionospheric heating facility; the waves were detected during a 2-min period, and the measurements indicated pulse-stretching by a few hundred msec, in conjunction with spectral broadening of about 10 Hz. The observed signal delays and pulse distortion are not consistent with expectations assuming propagation in a smooth magnetosphere between the assumed 'polar electrojet antenna' in the ionospheric D/E region and the 11,000-km altitude of the satellite. Scattering by density irregularities is judged the likely sources of the spectral broadening and delays.
TL;DR: In this article, the nonlinear power limiting processes in silica and air were investigated for picosecond pulses at the KrF wavelength, and a mechanism for the rapid spectral broadening in air based on Ramanenhanced four-wave mixing was proposed.
Abstract: The nonlinear power limiting processes in silica and air are investigated for picosecond pulses at the KrF wavelength. The two-photon absorption coefficient and the nonlinear refractive index in silica are measured to be 0·06 cm GW−1 and 1·7 × 10−13 e.s.u. respectively. A mechanism for the rapid spectral broadening in air based on Raman-enhanced four-wave mixing is proposed. Experimental evidence supporting this hypothesis is presented.
TL;DR: In this article, a layered synthetic microstructure (LSM) technology is used to build a simple, high-throughput, near-normal incidence soft x-ray spectrometer as a diagnostic for magnetically confined plasmas.
Abstract: With the recent advances in layered synthetic microstructure (LSM) technology, it is now possible to build a simple, high‐throughput, near‐normal incidence soft x‐ray spectrometer as a diagnostic for magnetically confined plasmas. Such spectrometers could be used for radiative power loss measurements from intrinsic impurities, an impurity concentration monitor, or ion temperature measurements from Doppler broadening of high charge‐state metallic impurities. LSMs have been developed as either flat or curved multilayer mirrors (MLMs) or as coatings for conventional gratings. Flat multilayer mirrors can have near‐normal incidence reflectivities greater than 50% throughout the entire soft x‐ray region with bandpasses that can be less than 4 A. Coated gratings are being developed that will combine the high soft x‐ray reflectivity of the LSM with the high resolution of the grating. Specific applications of LSMs as dispersive elements will be discussed. As an example, LSM‐based low‐resolution spectra of both a laboratory and tokamak plasma will be presented.
TL;DR: The transport of carbon and oxygen impurities has been studied in TEXTOR by introducing the gases CH and CO through a small hole in a test limiter as discussed by the authors, where the toroidal distributions of different charge states of the impurities have been measured using a CCD camera with optical filters.
TL;DR: In this paper, the authors measured the Doppler broadening of radiation from the annihilation of positrons in p+-silicon epilayers 1 and 0.4 mu m thick epitaxially grown at different temperatures.
Abstract: The Doppler broadening of radiation from the annihilation of positrons in p+-silicon epilayers 1 and 0.4 mu m thick epitaxially grown at different temperatures has been measured. The signal from positrons decaying within the epilayers is enhanced at the expense of any significant contribution from surface annihilation, enabling direct measurement of the Doppler lineshape parameter S characteristic of the epilayers. The epilayer S-value is observed to decrease for samples grown at temperatures below 700 degrees C, for which the expected concentration of oxygen defects increases. The correlation between S and oxygen concentration is interpreted in terms of (a) transition-limited trapping by atomic oxygen defects and (b) diffusion-limited trapping by SiOx precipitates. The former is consistent with secondary-ion mass spectrometry measurements if the specific trapping rate is reduced to at least half of the value quoted by earlier researchers; the latter implies that the results are consistent with the formation of SiO1.75 precipitates of mean radius 3.2+or-0.7 nm.
TL;DR: A theoretical model is used to show how the Doppler spectrum for various axisymmetric velocity profiles is affected by beam misalignment and incomplete insonation, and theoretical expressions and results are presented for the spectral broadening index (SBI), normalized spectral variance (NSV), coefficient of kurtosis (CK), and the coefficient of skewness (CS).
Abstract: A theoretical model is used to show how the Doppler spectrum for various axisymmetric velocity profiles is affected by beam misalignment and incomplete insonation. Results are presented for both circular and square beam geometries. Moreover, a closed-form expression is derived for the power spectral density received by an on-axis transducer with a Gaussian beam profile. It is shown that the error incurred in measuring the mean Doppler frequency with such a profile will generally be bounded by the results for the circular and square beam geometries. The effects of an ideal high-pass filter on the mean Doppler frequency and the backscattered Doppler power are examined. It is shown that such a filter can introduce large differences in the measured systolic to diastolic power ratios. Finally, theoretical expressions and results are presented for the spectral broadening index (SBI), normalized spectral variance (NSV), coefficient of kurtosis (CK), the coefficient of skewness (CS) as functions of the axisymmetric velocity profile shape assuming complete uniform insonation.
TL;DR: In this article, the gas density in axial electron cyclotron resonance (ECR) plasma device was measured with a small tube to an external capacitance manometer, and the results indicated a significant influence of gas temperature and rarefaction on the dynamics of plasma formation and ionization efficiency.
Abstract: Neutral gas density has been measured in both the source and sample regions of an axial electron cyclotron resonance (ECR) plasma device. The measurements involved sampling with a small tube to an external capacitance manometer. The gas density in the central ECR region was found to be strongly dependent on the applied power and to decrease approximately linearly with discharge power. At the maximum applied power of 1250 W, and at an Ar pressure of 0.7 mTorr, the gas density was reduced to 14% of its preplasma value, indicative of significant gas heating and rarefaction. This is equivalent to a gas temperature of 2500 K (0.2 eV), which is consistent with reported Doppler broadening optical emission measurements. At the sample region, approximately 35 cm from the ECR region, the gas density was reduced by gas heating to only 85% of its preplasma value. The electron density was measured in the ECR region by means of a commercial microwave interferometer device. Electron densities, integrated across the width of the chamber, reached ≂2×1012cm−3 at 1250 W and 0.7 mTorr Ar. The ionization fraction at 0.7 mTorr and 1250 W of applied power was 0.31, assuming an average electron density across the chamber. Indications point towards a localization of the plasma in the center of the chamber, which would indicate an ionization fraction of more than 0.50. These results suggest a significant influence of gas temperature and rarefaction on the dynamics of plasma formation and ionization efficiency. In addition, an isotropic, chemical component to many reactive etching systems must be anticipated due to the potentially high gas temperatures in and near the ECR region.
TL;DR: In this article, variable-energy positrons were used as a nondestructive probe for diamond films synthesized on the Si substrate from a gas phase of a CH4/H2 mixture by microwave plasma chemical vapor deposition.
Abstract: Variable-energy positrons were used as a nondestructive probe for diamond films synthesized on the Si substrate from a gas phase of a CH4/H2 mixture by microwave plasma chemical vapor deposition. The Doppler broadening of the annihilation photons was found to be strongly influenced by the concentration of CH4. The values of mean positron diffusion length in the diamond films were found to be decreased by increasing the concentration of CH4. The concentration of defects, C, was estimated as follows: 4×10-4
TL;DR: In this paper, the authors concentrate on positron lifetime and doppler broadening studies of electron irradiated Czochralski grown silicon (Cz-Si) heat treatment.
Abstract: Positron annihilation investigations of defects in semiconductors have been concentrated on silicon and gallium arsenide. Recent advances in the case of silicon coupled with EPR data has firmly established key parameters such as positron lifetimes associated with various vacancy clusters and positron trapping cross sections for different charge states of vacancies. This talk will concentrate on positron lifetime and doppler broadening studies of electron irradiated Czochralski grown silicon (Cz-Si) heat treatment of Cz-Si, heavily doped Cz-Si and plastically deformed Si.
TL;DR: In this paper, sound wave backscattering by turbulent water (free of particulates) in a water flume using a high resolution, 1.5 mm wavelength, Doppler sonar is presented and discussed.
Abstract: Observations of sound wave backscattering by turbulent water (free of particulates) in a water flume using a high resolution, 1.5 mm wavelength, Doppler sonar, are presented and discussed. The results show that the backscattering produced by water turbulence yields well defined Doppler spectra containing velocity variance information relevant to the study of water turbulence characteristics. Near the flume bed, the observed Doppler velocity spectrum width is greater than that expected from the turbulent velocity spectrum and other known sources of spectral broadening. The excess Doppler spectrum width may be explained assuming that the temperature structures acting as sonar targets tracing the velocity eddies, have a transient nature.
TL;DR: Spectra of the phase-noise-induced fluorescence-intensity fluctuations are shown to contain contributions from transients excited by the phase noise and are more sensitive to artifacts in the noise modulation process than the intensity spectrum of the laser field itself.
Abstract: We have measured the variance in fluorescence intensity and the spectrum of those fluctuations for two-level atoms in a phase-diffusing laser field. We compare our results with recent theoretical predictions that have been extended to include the effects of Doppler broadening and spatial variation of the laser intensity. Our study includes the effects of laser power, bandwidth, and shape (Lorentzian and non-Lorentzian) of the laser spectrum. At lower laser intensities, our measured variances versus detuning are in quantitative agreement with the theoretical predictions. At intensities above saturation, the variance is sensitive to inhomogeneities in the distribution of laser intensity in the interaction region, and only qualitative agreement is achieved. Asymmetries in the variance versus detuning resulting from correlated amplitude and phase noise have been observed. Spectra of the phase-noise-induced fluorescence-intensity fluctuations are shown to contain contributions from transients excited by the phase noise and are more sensitive to artifacts in the noise modulation process than the intensity spectrum of the laser field itself.
TL;DR: A general model for atomic memory effects is discussed and expressions for the noise correlation function, phase diffusion, and the emitted spectrum are derived that allow for a frequency distribution over the lasing atoms and hence account for Doppler broadening or a selective excitation of the atoms.
Abstract: We demonstrate how spontaneous-emission noise in lasers and masers can be reduced through memory effects of the lasing atoms. We show that for short measurement times the spontaneous-emission noise can be smaller than the usual Schawlow-Townes limit. We discuss a general model for atomic memory effects and derive expressions for the noise correlation function, phase diffusion, and the emitted spectrum. Furthermore, we allow for a frequency distribution over the lasing atoms and hence account for Doppler broadening or a selective excitation of the atoms.
TL;DR: In this paper, a variable-energy positron beam was used to study titanium implanted at ambient temperature with doses of 15 × 1016cm−2 100 keV krypton ions.
Abstract: Samples of titanium implanted at ambient temperature with doses of 15 × 1016cm−2 100keV krypton ions have been studied using a variable-energy positron beam. Doppler broadening measurements on the 511 keV photon spectra arising from positron annihilation at varying depths beneath the sample surface have revealed information on positron traps, trapping rates and diffusion lengths. Trapping over the depth range corresponding to the implanted krypton is consistent with the krypton bubble formation and associated damage detected by transmission electron microscopy. A new observation of interest is that positron trapping is found well beyond the implanted-ion range. Calculations using the TRIM code suggest that recoils can penetrate this region to give a significant amount of displacement damage. The resulting characteristic dislocation loop sub-structures, either alone or in combination with knocked-in end-of-range krypton atoms, provide the observed positron traps. This picture is consistent with th...
TL;DR: In this article, the temperature-, the current-, and the frequency dependences of conduction noise were studied at temperatures where the broadening of the resistive transition under the presence of magnetic field were observed.
Abstract: The temperature-, the current-, and the frequency dependences of the conduction noise were studied at temperatures where the broadening of the resistive transition under the presence of magnetic field were observed The result suggests that the broadening is mainly due to the enhancement of the fluctuation of superconductivity in two-dimensional CuO2 planes A sharp peak in the temperature dependence of the noise power was found at lower temperatures, which is likely to correlate with the melting of the flux lattice
TL;DR: A brief review is given of quantitative Doppler ultrasound techniques applied to arteries, with a focus on waveform analysis, volume flow measurement and colour flow imaging.
Abstract: A brief review is given of quantitative Doppler ultrasound techniques applied to arteries. Doppler ultrasound procedures can be split into waveform analysis, volume flow measurement and, recently, colour flow imaging. The pulsatility of the Doppler waveform has been used to assess distal vascular resistance. In the obstetric field the increase in pulsatility seen in the umbilical artery waveform when there is placental disease is a good predictor of fetal compromise. Considerable effort has been undertaken over the past 20 years in the assessment of carotid artery stenosis using Doppler. Both the peak systolic velocity in the internal carotid and spectral broadening have been related to the degree of stenosis. More complex waveform analysis methods such as principal component analysis have been used, however these have not passed into clinical practice. Measurement of volume flow in arteries using a duplex system is attractive, but in practice there may be large errors and this technique is not routinely performed. Recently cardiac output has been measured by a Doppler device using the attenuation-compensation principle. This promising technique is currently under assessment. Colour flow Doppler raises new prospects for quantitation in Doppler. At present the colour flow Doppler image is assessed by eye. Quantitative techniques in colour flow are likely to be introduced as experience with these systems grows.
TL;DR: In this paper, a variable energy positron beam and a Rutherford backscattering were used to study polycrystalline Pd and amorphous PdTa films on Al substrates.
Abstract: Polycrystalline Pd and amorphous PdTa films on Al substrates were studied by a variable energy positron beam and by Rutherford backscattering. Since positron diffusion in the overlayers is limited, the range follows directly from the Doppler broadening as a function of incident positron energy. To observe possible effects of positron backscattering, a sandwich of Al/Pd/Al was studied as well. It was found that the mean penetration depth is not described well by z(E)=A(μg/cm2)×En(E), if A and n are assumed to be material and energy independent.
TL;DR: In this paper, collision broadening and shift of the resonance line 6 2 S 1/2 -6 2 P 3/2 of Cs perturbed by each rare gas at temperature of 293 K were precisely measured with using a single mode diode laser.
Abstract: Collision broadening and shift of the resonance line 6 2 S 1/2 -6 2 P 3/2 of Cs perturbed by each rare gas at temperature of 293 K were precisely measured with using a single mode diode laser. The broadening and the shift measured at low gas pressures (below 200 mbar) of rare gas showed an excellent linear dependence on atomic density. The broadening and the shift constants are obtained and cross sections of the broadening and the shift are estimated. The broadening and the shift constants are compared with the previously obtained experimental and theoretical results. The cross sections are discussed as a function of atomic parameters of the rare gas.
01 Nov 1990
TL;DR: In this article, a theoretical and experimental study of the influence of spectral broadening on the pulsed Doppler spectrum is presented, with particular emphasis placed on the effect of sample volume size and position on the spectrum.
Abstract: A theoretical and experimental study of the influence of spectral broadening on the pulsed Doppler spectrum is presented. Specifically, the effect of sample volume size and position on the spectrum is discussed with particular emphasis placed on how these parameters alter the spectral broadening index. A parabolic flow profile was assumed.
02 Jan 1990-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the behavior of hydrogen atoms adsorbed on tungsten crystal surfaces is surveyed with respect to the Doppler broadening of the very narrow 6.4 MeV 1 H(15 N, αγ) 12 C resonant nuclear reaction.
Abstract: The Doppler broadening of the very narrow 6.4 MeV 1 H( 15 N, αγ) 12 C resonant nuclear reaction is discussed and surveyed with respect to the behavior of hydrogen atoms adsorbed on tungsten crystal surfaces. For the (001) surface, the thermal vibration energy of the hydrogen atoms is definitely obtained. However, for the (110) surface, the resonance line shape is much wider than would be expected by the Doppler broadening contribution alone. This result may suggest that the stable site of the adsorbed hydrogen is not only on the surface but also inside the crystal.