scispace - formally typeset
Search or ask a question

Showing papers on "Doppler broadening published in 1982"


Journal ArticleDOI
TL;DR: Tanaka and Venkateswaran as discussed by the authors used the linear theory of cross-field or gradient-drift instability to explain the field-aligned irregularities in middle latitude E s -layers.

71 citations


Journal ArticleDOI
TL;DR: In this article, the authors observed Al L/sub 2,3/ Auger electrons from clean aluminum surfaces bombarded by mass-analyzed beams of noble-gas ions at 45/sup 0/ incidence, and in the energy range 600 eV--15 keV.
Abstract: We have observed Al L/sub 2,3/ Auger electrons from clean aluminum surfaces bombarded by mass-analyzed beams of noble-gas ions at 45/sup 0/ incidence, and in the energy range 600 eV--15 keV. The electron energy spectra show a wide structure similar, though not identical, to those observed under electron impact, and sharp lines. These lines are identified as resulting from the Auger decay of 2p-excited Al and Al/sup +/. The decay occurs in vacuum from sputtered particles, as suggested by the asymmetric Doppler broadening of the Auger lines. The Auger yields can be scaled when plotted against the maximum energy transfer in a projectile-Al collision, indicating that the excitation occurs mainly in symmetric collisions between target atoms. Exceptions are the cases of impact with He/sup +/ and low-energy Ne/sup +/ ions where projectile-Al collisions are responsible for the excitation, possibly by two-electron transitions.

70 citations


Journal ArticleDOI
TL;DR: In the clinical study, 162 cases were examined using a 4 MHz Doppler system and by standard four-vessel arteriography, and Spectral broadening, evaluated by subjective grading, yielded similar results.
Abstract: The results of in vitro and in vivo studies to determine the application and limitations of frequency analysis for CW Doppler ultrasound assessment of carotid stenoses are reported. In the in vitro study, the peak Doppler frequency and a new spectral broadening index were determined proximal to, at, and distal to axisymmetric and asymmetrical model stenoses. Good correlations with percent area stenoses were found. In the clinical study, 162 cases were examined using a 4 MHz Doppler system and by standard four-vessel arteriography. Peak frequencies of greater than 3.8 KHz were diagnostic of internal carotid stenoses of 3.2 mm minimum lumen diameter or less, with a sensitivity of 92% and a specificity of 94%. Spectral broadening, evaluated by subjective grading, yielded similar results.

69 citations


Journal ArticleDOI
TL;DR: In this paper, a new compact system has been developed to produce monoenergetic positrons of variable energy, which can be used to investigate defects and defect structures close to the surface in metals and alloys.
Abstract: A new compact system has been developed to produce monoenergetic positrons of variable energy. The energy range available at present is between 150 eV and 28 keV, so that depth profiles can be measured. This positron beam is being used to investigate defects and defect structures close to the surface in metals and alloys. The technique of Doppler broadening of the annihilation radiation is applied for these measurements.

57 citations


Journal ArticleDOI
TL;DR: In this article, a simulation of ion broadening in an Ar + -plasma (N e = 7.2 × 10 16 cm −3, T = 12,200 K ) with full account of radiator motion is presented.
Abstract: For the hydrogen line L-β, broadening in an Ar + -plasma ( N e = 7.2 × 10 16 cm −3 , T = 12,200 K ) has been investigated with the help of a computer simulation of ion broadening taking full account of radiator motion. The anisotropy in Stark broadening for a moving radiator is found to be negligible under these conditions, but Stark profiles depend markedly on the radiator speed. The final line profile (including Stark and Doppler broadening) is nearly the same as the profile obtained by convolution of the Doppler profile with the Stark profile for radiators at rest and fictitious ions with the reduced mass of the atom-ion pair.

46 citations


Journal ArticleDOI
TL;DR: In this paper, a theory for the resonant excitation of a high-lying atomic or molecular state by the absorption of n photons from up to n different lasers is presented.

46 citations


Journal ArticleDOI
J. Botineau1, Roger H. Stolen1
TL;DR: In this paper, it is shown that spectral self-broadening can be treated as self-phase modulation or three-wave mixing, and that these are simply different representations for the same process.
Abstract: It is shown by theory and experiment that spectral self-broadening in optical fibers is enhanced in fibers that maintain linear polarization. Spectral self-broadening can be treated as self-phase modulation or three-wave mixing, and we show that these are simply different representations for the same process.

43 citations


Journal ArticleDOI
TL;DR: Practical aspects of a method for estimating the mean velocity waveform for a CW ultrasound system that generates an analog mean signal for both forward and reverse flow are described.
Abstract: Practical aspects of a method for estimating the mean velocity waveform for a CW ultrasound system are described. The method, based on the technique proposed by Gerzberg and Meindl (1977), generates an analog mean signal for both forward and reverse flow with an accuracy of better than ± 5%. Application of the circuit for arterial assessment are presented, and its potential use for determining carotid spectral broadening is considered.

38 citations


Journal ArticleDOI
TL;DR: Foreign-gas broadening coefficients have been measured for selected lines of ozone and several R -branch lines of nitric oxide using a computerized tunable diode laser spectrometer and showed the importance of fitting a Lorentzian line shape out to several times the halfwidth to obtain a correct value of the broadening coefficient.
Abstract: Foreign-gas broadening coefficients have been measured for selected lines of ozone in the 9.2 micron region and for several R-branch lines of nitric oxide in the 5.4 micron region using a computerized tunable diode laser spectrometer. The data analysis showed the importance of fitting a Lorentzian line shape out to several times the halfwidth to obtain a correct value of the broadening coefficient. The measured broadening coefficients of nitric oxide were in good agreement with those obtained by Abels and Shaw (1966). The results of the analysis of eleven lines in the v-1 band and five lines in the v-3 band of ozone show a transition-dependent broadening coefficient. The average value of the foreign-gas broadening ceofficients for the measured v-1 and v-3 lines are 0.075 and 0.073 per cm per atm, respectively.

38 citations


Journal ArticleDOI
TL;DR: In this article, the Larmor radius wave was measured in a warm toroidal plasma with externally launched ion Bernstein waves detected by CO/sub 2/ laser scattering and radial scanning of the laser beam allowed precise determination of k/sub perpendicular/ for the finite ion Larmour radius wave (..omega..< or approx. =2..cap omega../sub i/).
Abstract: Hydrogen ion temperature has been measured in a warm toroidal plasma with externally launched ion Bernstein waves detected by CO/sub 2/ laser scattering. Radial scanning of the laser beam allows precise determination of k/sub perpendicular/ for the finite ion Larmor radius wave (..omega..< or approx. =2..cap omega../sub i/). Knowledge of the magnetic field strength and ion concentration then give a radially resolved ion temperature, independent of T/sub e/. Probe measurements and Doppler broadening of Ar II 4806 A give excellent agreement.

31 citations


Journal ArticleDOI
TL;DR: In this article, the linewidth and lineshape of the zero phonon line corresponding to the 0 → 1 vibrational transition of CO in solid N 2 has been studied as a function of the relevant parameters: thermal history of the sample, concentration and temperature.

Journal ArticleDOI
TL;DR: In this article, the steady-state probe absorption line-shape function for a strongly driven, Zeeman-degenerate molecular system was derived for the cases of parallel and perpendicular linear polarization of the two laser pairs.
Abstract: We calculate the steady-state probe absorption line-shape function for a strongly driven, Zeeman-degenerate molecular system. The probe laser is treated to lowest order while the pump laser is dealt with to all orders. We obtain the probe line shape for the cases of parallel and perpendicular linear polarization of the two lasers. As expected, the effects of M degeneracy, as well as differences due to the relative laser polarizations, are most pronounced when Doppler broadening is not important. However, even in the presence of large Doppler broadening we find a narrowing of the population hole by including the Zeeman degeneracy and a further narrowing if perpendicular laser polarizations are used.

Book ChapterDOI
TL;DR: In this article, the authors discuss applications of Resonance ionization spectroscopy (RIS) methods to atomic and molecular physics, and the possible use of RIS techniques in conjunction with pulsed supersonic nozzle jet beams is illustrated with a couple of experiments.
Abstract: Publisher Summary Resonance ionization spectroscopy (RIS) can be defined as a state-selective detection process in which pulsed tunable lasers are used to promote transitions from the selected state of the atoms or molecules in question to higher states, one of which will be ionized by the further absorption of another photon. At least one resonance step is used in the stepwise ionization process, and it has been shown that the ionization probability of the spectroscopically selected species can nearly always be made close to unity. The ability to make saturated RIS measurements opens up a wide array of applications to both basic and applied research. The chapter discusses applications of RIS methods to atomic and molecular physics. It begins with a theoretical description of multiphoton excitation using broad bandwidth lasers with a twofold purpose. First, the theoretical results are used to estimate excitation probabilities with regard to the feasibility and expected signal magnitude of the experiments discussed. Second, the results of these experiments can, in turn, be used to test various aspects of the theory such as atomic structure calculations and the model chosen to describe the laser radiation. A variety of photophysics and collision physics experiments on inert gases are suggested and described. The results of an experiment on the two-photon excitation of Xe are also discussed in the chapter. The possible use of RIS techniques in conjunction with pulsed supersonic nozzle jet beams is illustrated with the proposal of a couple of experiments.

Journal ArticleDOI
TL;DR: Polarization properties of phase-conjugate (PC) mirrors obtained by degenerate four-wave mixing in resonant gas media are experimentally analyzed and theoretically interpreted and it is shown that these properties are rather insensitive to the relaxation processes in the gas phase.
Abstract: Polarization properties of phase-conjugate (PC) mirrors obtained by degenerate four-wave mixing in resonant gas media are experimentally analyzed on various neon transitions and theoretically interpreted. We show that, because of the Doppler broadening of the decay rate of the gratings, these properties are rather insensitive to the relaxation processes in the gas phase. We demonstrate simple ways of characterizing PC mirrors with either λ/2 birefringence (for cross-polarized pumps) or J-dependent linear dichroism (for parallel-pump polarization).

Journal ArticleDOI
TL;DR: In this paper, the resonance Raman excitation profiles for the ν1, ν2, and ν3 vibrations of lycopene in ethyl alcohol, toluene, and carbon disulfide solvents have been measured.
Abstract: The resonance Raman excitation profiles for the ν1, ν2, and ν3 vibrations of lycopene in ethyl alcohol, toluene, and carbon disulfide solvents have been measured. The results are interpreted in terms of a three‐mode vibrational theory which includes both homogeneous and inhomogeneous broadening effects. Excellent agreement between calculated and observed excitation profiles and visible spectra was found, thus emphasizing the need to interpret resonance Raman data using a multimode vibrational model. The results indicate that the major broadening mechanism is homogeneous broadening, with about a 25% contribution from inhomogeneous broadening. The excitation profiles in carbon disulfide gave the largest inhomogeneous broadening.

Journal ArticleDOI
TL;DR: In this paper, a theory of Stark broadening in plasmas is presented in which the effects of broadening by ion perturbers are treated in a manner similar to the relaxation theory or unified theory for electrons.
Abstract: A theory of Stark broadening in plasmas is presented in which the effects of broadening by ion perturbers are treated in a manner similar to the relaxation theory or unified theory for electrons. An expression is derived for Fano's broadening operator M ( ω ) which does not contain the projection operators or cumulants of previous forms. To obtain a calculable expression for M ( ω ), an approximation is made in which small, second-order fluctuation terms are replaced by their adiabatic limits. Sample calculations are presented for the first two members of the Lyman and Balmer series of hydrogen which show reasonable agreement with experiment, although the “dip” of the β-lines is still too pronounced.

Journal ArticleDOI
TL;DR: In this paper, a systematic exposition of the qualitative problems of nonlinear laser resonance spectroscopy, taking into account the effect of the light field on the dynamics of the broadening collision and, correspondingly, on the rate of phase relaxation, is presented.
Abstract: This review gives a systematic exposition of the qualitative problems of nonlinear laser resonance spectroscopy, taking into account the effect of the light field on the dynamics of the broadening collision and, correspondingly, on the rate of phase relaxation. The results of experiments, in which these nonlinear optocollisional effects, predicted earlier theoretically, were observed, are presented briefly.

Journal ArticleDOI
TL;DR: In this paper, the resolving power of convex curved crystal spectrographs was derived as a function of the linear source size parallel to the plane of dispersion and the Bragg angle.
Abstract: Ray tracing techniques are used to derive an analytic approximation for the resolving power, λ/Δλ, of convex curved crystal spectrographs as a function of the linear source size parallel to the plane of dispersion and as a function of the Bragg angle. Using the derived expression, we investigate source size broadening in spectra from spatially and temporally integrated imploding‐wire plasmas. We also compare the level spacing between the last discrete spectral line and the spectral line succeeding it to various line broadening processes: line broadening due to the finite size of the plasma source (source size line broadening), Doppler broadening, and line broadening due to the crystal rocking curve. We show that, in some cases, source size line broadening is comparable to the level spacing. Source size line broadening causes difficulties in obtaining the ion density from the series merging technique, since the latter is based on Stark broadening. We show that in some previously reported experiments the io...

Journal ArticleDOI
TL;DR: Positron trapping at structural defects in lead, tin and some lead-tin alloys has been studied by measurements of the temperature dependence of the Doppler broadening of the annihilation photon line as discussed by the authors.
Abstract: Positron trapping at structural defects in lead, tin and some lead-tin alloys has been studied by measurements of the temperature dependence of the Doppler broadening of the annihilation photon line. Monovacancy formation enthalpies have been deduced from the data. In a Pb-8 at.% Sn alloy a sharp transitory peak in the peak height to area ratio or S parameter is observed some 20 degrees below the solvus temperature. An interpretation is offered in terms of enhanced positron trapping at grain boundary sites associated with the initial stages of tin precipitation.

Journal Article
TL;DR: The accuracy of Doppler spectral analysis for diagnosing stenoses of the carotid artery was evaluated in this study and Spectral broadening, evaluated by subjective grading, yielded similar results.
Abstract: The accuracy of Doppler spectral analysis for diagnosing stenoses of the carotid artery was evaluated in this study. Two hundred and five patients were examined, using a 4 megahertz continuous wave Doppler velocity meter and a real-time frequency analyzer. By a comparison of the results of arteriography, peak Doppler frequencies of greater than 3.8 kilohertz were diagnostic of internal carotid artery stenoses having residual lumen diameters of 3.2 millimeters, or less, with a sensitivity rate of, 91 per cent and a specificity rate of 92 per cent. Spectral broadening, evaluated by subjective grading, yielded similar results.

Journal ArticleDOI
TL;DR: In this article, the impact broadening of strontium 5sns 1S0, 5snd 1D2 and 5 snd 3D2 levels by He and Xe has been studied by measuring the collisional halfwidths of Doppler-free two-photon absorption lines from the 5s21S0 ground state in a thermionic diode.
Abstract: The impact broadening of strontium 5sns1S0, 5snd1D2 and 5snd3D2 levels by He and Xe have been studied by measuring the collisional half-widths of Doppler-free two-photon absorption lines from the 5s21S0 ground state in a thermionic diode. Large inelastic contributions to the broadening rates of the levels have been found where the moduli of the quantum defects of different level series are close to each other. A similar but continuousn-mixing behaviour along the series has also been found in our recent investigation on the broadening of Rb levels by noble gases. The broadening rates of the very high levels in Sr were found to be independent on the principal quantum number and the angular momentum of the levels and in good agreement with our recent broadening data of the Rb-He and Rb-Xe systems and the data for Na-He and Na-Xe found by the Columbia group.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the detection limit for second harmonic detection is of the same order as for first harmonic detection: the modulation depth must be approximately the full linewidth of the line profile.
Abstract: The theory for frequency modulation given by Karplus has been extended to include Doppler broadening and arbitrarily large modulation depths. It is shown that the detection limit for second harmonic detection is of the same order as for first harmonic detection: the modulation depth must be approximately the full linewidth of the line profile. Procedures are discussed for extracting from experimental data the linewidth and center frequency of an absorption line with a Voigt profile. At zero detuning information about collisional line broadening can be obtained from the dependence of the second harmonic signal upon the modulation depth. Some experimental examples in the microwave region are presented as a test of the theory. Measurements on the rotational transition J = 2 → 3 (v2 = 1) of OCS yield collisional self-shift and self-broadening parameters of −0.14 (±0.01) and 5.97 (±0.01) MHz/Torr, respectively; these values are in accordance with literature but are more accurate. For the line center at zero pressure a much more accurate value of 36 571 422.0 ± 0.7 kHz has been found, which is in agreement with recent theoretical calculations.

Journal ArticleDOI
TL;DR: High-resolution cw coherent anti-Stokes Raman spectra of the nu(1) Q branch of methane in an underexpanded supersonic jet at temperatures as low as 31.5 K and pressures below 2 Torr are obtained.
Abstract: High-resolution CW coherent anti-Stokes Raman spectra of the nu1 Q branch of methane in an underexpanded supersonic jet were obtained at temperatures as low as 31.5 K and pressures as low as 2 torr. The experimental spectra were well fitted by the calculated theoretical spectra, including transit-time broadening. A temperature of 31.5 K produced the best fit to the data, and the transit-time broadening was comparable to the residual Doppler broadening of about 100 MHz. The supersonic jet provides a convenient method of obtaining molecular cooling at relatively high density, and the ease of construction and the wide range of temperatures and densities available make it a useful tool for high resolution molecular spectroscopy.

Proceedings ArticleDOI
01 Jan 1982
TL;DR: In this paper, a method of quantification based on extractinq the instantaneous maximum and a mean spectral waveforms is described, where the degree of disturbed flow is estimated from a spectral broadening index (maximum-mean/maximum).
Abstract: Chanaes in the Doppler spectrum arising from disturbed flow, particularly in the carotid arteries, are difficult to assess in a reliable manner. This paper describes a method of quantification based on extractinq the instantaneous maximum and a mean spectral waveforms. The degree of disturbed flow is estimated from a spectral broadening index (maximum-mean/maximum) . Both the maximum and mean are obtained diqitally and the spectral broadening index waveform is computed in real time. Experimental results are shown using an in vitro model that closely approximates the carotid flow conditions. The index, when measured at peak SYStole a t points just beyond a stenosis correlate quite well w ith the percent area stenosis.

Journal ArticleDOI
TL;DR: In this article, the authors used interferometric observations on the green coronal line (λ 5303 a) carried out during the total solar eclipse of 1980 February 16 have yielded relative Doppler shift velocities with an accuracy of ± 7 km s-1.
Abstract: Fabry-Perot interferometric observations on the green coronal line (λ 5303 a) carried out during the total solar eclipse of 1980 February 16 have yielded relative Doppler shift velocities with an accuracy of ± 7 km s-1. The values show a peak in the 30–50 km s-1 range indicating largescale macroscopic mass motion in the solar maximum corona.

Journal ArticleDOI
TL;DR: In this article, the authors show that the residual Doppler broadening of a two photon absorption line can be compensated by velocity dependent light shifts, and they report the results of an experiment performed on 20 Ne atoms and giving evidence for this compensation effect.

Journal ArticleDOI
TL;DR: In this article, an expansion for the absorption line shape of a two-level system in a strong radiation field being perturbed by dephasing collisions with a thermal bath of foreign atoms is presented.
Abstract: We develop an expansion for the absorption line shape of a two-level system in a strong radiation field being perturbed by dephasing collisions with a thermal bath of foreign atoms. We assume that the bath atoms do not interact with the radiation field and with each other. The microscopic information relevant for line broadening in a strong field is expressed in terms of a hierarchy of dipole correlation functions. The latter may be calculated with the use of the Franck-Condon factors for the nuclear wave functions. The present theory reduces in the weak-field limit to the well-known linear unified theory of line broadening and in the impact limit we recover the Karplus-Schwinger formula.

Journal ArticleDOI
TL;DR: In this article, the Schweizer-Chandler theory of vibrational dephasing is used to compute absolute inhomogeneous broadening linewidths for methyl stretches.
Abstract: The dependence of inhomogeneous vibrational linewidth broadening on attractive forces form slowly varying local liquid number densities is examined. The recently developed Schweizer–Chandler theory of vibrational dephasing is used to compute absolute inhomogeneous broadening linewidths. The computed linewidths are compared to measured inhomogeneous broadening linewidths determined using picosecond vibrational dephasing experiments. There is a similarity between correlations of the Schweizer–Chandler and George–Auweter–Harris predicted inhomogeneous broadening linewidths and the measured inhomogeneous broadening linewidths. For the methyl stretches under investigation, this correspondence suggests that the width of the number density distribution in the liquid determines the relative inhomogeneous broadening magnitudes. (AIP)

Journal ArticleDOI
TL;DR: In this article, the degrees of first and second-order coherence and the spectral distribution of the light emitted in resonance fluorescence by a two-level atom driven by monochromatic incident light were investigated.
Abstract: Calculations are presented for the degrees of first- and second-order coherence and the spectral distribution of the light emitted in resonance fluorescence by a two-level atom driven by monochromatic incident light. The theory includes the effects of both homogeneous and inhomogeneous broadening, but is restricted to ranges of the parameters for which analytic solutions can be obtained. There is a further restriction to forward scattering in the case where the inhomogeneous broadening is caused by the Doppler effect. The results show marked differences between the effects of the homogeneous and inhomogeneous broadening mechanisms.

Journal ArticleDOI
01 Dec 1982
TL;DR: In this paper, a grating of high groove density in a 2m grazing-incidence monochromator was used to reduce the asymmetric line broadening in high-resolution spectra of fast ion beams.
Abstract: In high-resolution spectra of fast ion beams, employing a grating of high groove density in a 2m grazing-incidence monochromator, asymmetric line broadening has been observed. The effect is explained in terms of Doppler broadening and atomic lifetimes. Various procedures to reduce the broadening by narrowing the angular acceptance of the detection system have been applied.