Doppler Contribution Research Articles

Experimental and theoretical investigation of neonlike selenium x-ray laser spectral linewidths and their variation with amplification.

This paper describes our recent x-ray laser spectral linewidth measurements and discusses the consequences of these measurements. The experiments observed the 206.38- and 182.45-\AA{} laser transitions in neonlike selenium using an extremely high-resolution soft-x-ray spectrometer, and measured the spectral linewidths and relative spectral intensities of the laser lines from amplifiers of varying lengths. The data allow the intrinsic (unamplified) linewidths of the 206- and 182-\AA{} lasers to be extrapolated as 50 and 35 m\AA{}, respectively. The intrinsic spectral width of the 206-\AA{} laser is somewhat greater than the predicted 43-m\AA{} Voigt-profile width based on calculated transition rates and on the expected ion temperature in the plasma, and while the number of data points obtained with the 182-\AA{} laser is small and a conclusive comparison with calculations is not possible, the extrapolated intrinsic linewidth of this laser is clearly consistent with the predicted 37-m\AA{} Voigt-profile width and is not significantly broader or narrower than expected. The data also show significant gain narrowing of both lines with increasing amplifier length and show no significant rebroadening of the 206-\AA{} laser in long, saturated amplifiers. We discuss line broadening and line transfer calculations we have performed which show that the saturated 206-\AA{} laser line transfer behavior can be treated homogeneously due to non-negligible homogeneous lifetime broadening contributions, which significantly reduce inhomogeneous Doppler saturation rebroadening, and due to collisional redistribution rates which are large enough in any case to homogenize the otherwise inhomogeneous Doppler contributions. We also discuss the implications of these results with regard to earlier suggestions that Dicke narrowing effects could play a significant role in determining the intrinsic line profiles of these laser transitions, and we conclude that Dicke narrowing effects are not likely to be significant for either laser.

Concentration-modulated absorption spectroscopy: profiles of the Na D lines in a hydrocarbon flame

The potential value of pump-probe spectroscopy for the study of the spectral profiles of narrow gas-phase absorption lines has been investigated using the technique of concentration-modulated absorption spectroscopy (COMAS). The relationship of the probe laser 'gain' to the absorption line profile is established and the parameters of the Voigt line profile for the 3p2P12 /-3s2S12 / transition of atomic sodium in a hydrocarbon flame have been determined. The effects of a significant reduction in the Doppler contribution to the linewidth of this transition in the flame are clearly identified.

Contributions of color Doppler to the evaluation of cardiovascular abnormalities in the fetus

The applications of color Doppler sonography are reviewed in this article. Color Doppler is an efficient and time-saving means of assessing normal and abnormal flow in the fetus, making it an essential part of the echocardiographic examination for fetal congenital heart disease. In survey mode, color Doppler can be used to quickly evaluate whether flow channels are normal and to detect abnormal flow patterns. These abnormal flow patterns can then be examined further by pulsed or continuous wave Doppler, if needed. Color Doppler, which is subject to less rib shadowing than other Doppler techniques, also can help in assessing the fetal heart when there is less-than-adequate gray scale imaging.

Determination of the Electron Density in an Argon Laser Plasma by Spectroscopy of the Hydrogen Hα and Hβ Lines

AbstractFrom measurements of the Hα and Hβ spectral line profiles in a plasma, a method is developed which allows to separate the contributions of Doppler and Stark broadening. This method is superior to the deconvolution of Voigt profiles, in particular, when the lines are of low intensity. The electron density in the plasma can be calculated from the Stark broadening.An example is the low pressure (p ≈ 1 hPa) arc discharge of argon ion lasers which is characteristised by electron densities of approximately 1014 cm−3 at heavy particle temperatures of about 104 K. These plasma parameters lead to a broadening of the Balmer Hα and Hβ spectral lines of hydrogen, which has a low concentration within the discharge area. The spectral lines are broadened due to the electron density dependent Stark effect and the temperature responsive Doppler effect. The results are consistent with predictions of the argon ion laser modelling.

Prenatal diagnosis of cleft palate: contribution of color Doppler ultrasound.

The antenatal diagnosis of cleft palate by ultrasound can sometimes be difficult by conventional B-mode imaging, especially when the tongue is in its normal position. We describe two cases which illustrate the value of color Doppler in the antenatal diagnosis of cleft palate. In the first case, at 32 weeks' gestation, there was a large defect with a massive passage of flow extending from the buccal cavity into one of the nasal fossae. In the second case, at 22 weeks' gestation, a parasagittal view demonstrated the fetal tongue to be in the normal position, but there was an abnormal trajectory off low from the buccal cavity into one of the nasal fossae followed by an exit at the level of the cleft. Although a cleft lip was demonstrated on B-mode imaging, we would not have been able to make the diagnosis of cleft palate without color Doppler. This is the first report describing the contribution of color Doppler to the antenatal diagnosis of cleft palate.

Contribution of concurrent Doppler and EEG in differentiating occipital epileptic discharges from migraine

In a young woman, episodes of visual symptoms were accompanied by simultaneous nonspecific EEG alterations. Concurrent Doppler sonography showed increased blood flow velocity with latency of a few seconds in the posterior cerebral arteries only. This is typical for local autoregulatory hyperperfusion due to increased neuronal activity, thus indicating focal epileptic discharges and excluding migrainous attacks.

Simultaneous forward–backward Raman scattering studies of D2 broadened by D2, He, and Ar

Unavoidable beam crossings within a spherical-mirror, multipass stimulated Raman gain cell give rise simultaneously to forward- and backward-scattering Raman signals. In the Doppler-broadened/Dicke-narrowed regime of density, the lineshape is a function of the momentum transfer in the scattering process and thus the observed spectra will have more complex lineshapes than those seen with simple forward or backward scattering geometries. The analyses necessary to quantitatively account for such forward–backward spectra are summarized. These spectra enable unique experimental tests of the lineshape functions used for the description of the Raman Q-branch spectrum under conditions where Doppler contributions and Dicke narrowing are significant. Results for the D2:D2 and D2:He systems support the well-known Galatry, or soft collision, lineshape function. However, in the case of D2:Ar, our results suggest the need to employ the more general, complex soft collision function. In addition, these studies have provided data on linear-with-density line broadening coefficients (previously published) and line shifting coefficients (reported here) for these molecular systems.

An algorithm for determining dispersion and Doppler line widths from limited experimental data

We present an algorithm that allows the efficient determination of the dispersion and Doppler contributions to a Voigt profile from limited experimental data. For this purpose, we use the measured intensity profiles, as well as their first and second derivatives.

Effect of the Great Attractor on the cosmic microwave background radiation

ANISOTROPY in the cosmic microwave background radiation (CMB) is expected as a result of fluctuations in gravitational potential caused by large-scale structure in the Universe. The background radiation is redshifted as it climbs out of gravitational wells (the Sachs–Wolfe effect1). Here we present a map of the anisotropy in CMB temperature δT/T of our region of the Universe as viewed by a distant observer, predicted on the basis of the gravitational potential field. We calculate this field in the vicinity of the Local Group of galaxies from the observed peculiar (non-Hubble) velocities of galaxies, under the assumption that the peculiar motions are induced by gravity2–4. If the cosmological density parameter Ω is 1, the gravitational potential field of the Great Attractor and surrounding regions produces a maximum Sachs–Wolfe anisotropy of δT/T = (1.7 ± 0.3) x 10–5 on an angular scale of 1°. Doppler and adiabatic contributions to this anisotropy are expected to be somewhat larger. If similar fluctuations in the gravitational potential are present elsewhere in the Universe, the anisotropy present when the CMB was last scattered should be visible from the Earth, and should be detectable in current experiments5. A fundamental test of whether gravity is responsible for the generation of structure in the Universe can be made by looking for the imprint in the CMB of deep potential wells similar to those found in our neighbourhood6.

Limits on rotation-induced characteristics of radiation from stable rapidly rotating neutron stars

view Abstract Citations (4) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Limits on Rotation-induced Characteristics of Radiation from Stable Rapidly Rotating Neutron Stars Datta, B. ; Kapoor, R. C. Abstract Results are presented of a study of frequency shifts in radiation from the surface of rapidly rotating neutron stars and rotation-induced spectral line broadening as a function of their mass. It is found that, despite large rotation rates, the gravitational effects dominate over the Doppler contribution to the frequency shifts over the allowed mass range of a stable rotating neutron star. Astrophysical implications of effect of large rotation on spectral line characteristics are also discussed. Publication: The Astrophysical Journal Pub Date: August 1988 DOI: 10.1086/166599 Bibcode: 1988ApJ...331..784D Keywords: Gravitational Effects; Neutron Stars; Spectral Line Width; Stellar Radiation; Stellar Rotation; Doppler Effect; Emission Spectra; Gamma Ray Bursts; Stellar Mass; Astrophysics; STARS: NEUTRON; STARS: ROTATION full text sources ADS | data products SIMBAD (1)

Ion-motion broadening of the Delta n=0,n=2 transitions of C V in a carbon laser-produced plasma.

We measured the line profiles of the \ensuremath{\Delta}n=0,n=2 lines of C v produced when a ruby laser was focused (\ensuremath{\ge}${10}^{12}$ W/${\mathrm{cm}}^{2}$) onto a polyethylene target. Line profiles were measured at 3 mm from the target surface where the electron density is of the order of ${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ as inferred from a folded wave-front shearing interferometric technique and the line profile of the 3434-A\r{} line of C vi. After fitting the data to profiles calculated considering the different Stark and Doppler contributions to the line, we found that the calculated profile for the 3526-A\r{} line of C v is considerably narrower than the experimental result and this discrepancy is common to all the \ensuremath{\Delta}n=0,n=2 lines. Judging from the fact that the ratio of the experimental widths of the different lines is proportional to the respective ratio of wavelengths this effect should be related to the ion motion. The presence of hydrodynamic turbulence causing the profile to have a large effective Doppler temperature approximately equal to 600 eV may explain this result.

Double optical resonance at high pressure: Collisional broadening and doppler effects on ac stark splitting

The article presents the density matrix theory describing a three-level system in single- or multi-photon resonant interaction with two finite-bandwidth lasers and subject to high pressure. Under the steady-state and the weak-probe approximations, analytic solutions for the excitation spectra and the conditions for resolving the ac Stark splitting (also known as the Autler-Townes effect) are given. Calculations show that the resolution of the ac Stark doublet, observed in the two-color, three-photon 1s→3p excitation spectra of atomic hydrogen produced in H 2/air atmospheric-pressure flames, is greatly improved by eliminating the Doppler contribution of the 1s→2s two-photon transition. It is found that as pressure is increased, the asymmetry parameter of the doublet decreases; and at high enough pressure (e.g. several atm), the doublet becomes one broad resonance.

A technique for almost Doppler-free spectroscopy of highly ionised atoms

A technique is described which uses “longitudinal” observation of a recoil-ion source and offers the promise of high spectral resolution for highly ionised atoms. Transitions in helium-like neon have been observed from which an estimate of the Doppler contribution to the linewidth has been made.

Dicke Narrowing Reduction of the Doppler Contribution to a Line Width

In the simplest kinetic models of collisional narrowing or reduction of the Doppler contribution to a spectral line width, the narrowing process is related to the usual diffusion constant of transport theory. Dicke narrowing requires a correlation between the pre- and post-collisional absorber or emitter electric dipole moment. Pressure broadening on the other hand results from at least a partial destruction of this correlation so that in general pressure broadening and Dicke narrowing are statistically dependent on and correlated with each other. It follows that a spectroscopic diffusion constant is required. A classical phase description (which is easily converted to a semiclassical one) is used here to derive a kinetic equation for which the approximate line shape is obtained by It velocity moment method. The spectroscopic diffusion constant closely resembles the Chapman-Enskog first approximation for the diffusion constant but has mixed in an extra function (the memory) which represents the correlation between collision-induced changes of the dipole moment and velocity changes and the correlation between the pre- and post-collision electric dipole moment. Dicke narrowing can be used to obtain information about the line broadening amplitude SB(b, w) for strong velocity-changing collisions. The Galatry ('weak' collision) and 'strong' collision line-shape functions are obtained as different cutoff approximations in the velocity moment analysis. The present analysis, however, is not limited to specifically weak or strong collisions. The two line-shape formulae are shown to be virtually identical sufficiently far from the line centre and at sufficiently high densities. Convenient, approximate analytical formulae for the half-width are obtained using two different definitions.

Optical bistability in a resonant two-photon absorber

Optical bistabflity as a kind of first-order phase transition has been suggested and experimentally observed in an optical feedback system (1) as well as in a resonant absorber within an interferomcter ([ 2). A multiple-pass interferometer with a suitable nonlinear dispersive or absorptive mechanism can behave as a bistable optical system. The first suggestion was made by SZ6K~ et al. (1), and different versions have been shown to work with the nonlinearity due either to an atomic medium at resonance with the impinging field (2) or to an external feed-back system (3). We are here interested in the optical bistability arising from the collective behaviour of an atomic system. A general theory has been formulated in a series of papers by BONIFACIO and LVGIATO (4) to obtain absorptive and dispersive atomic bistability. As is well known from the first approaches (3) a difficulty of atomic bistability consists in inhomogeneous broadening due to the Doppler contribution of atom in a cell. We show here evidence of a bistable behaviour of an interferometer filled with a two-photon absorber and working in a travelling wave mode. This is the first step to derive, afterwards, a Doppler free atomic bistability (6) by absorbing photons from opposite directions and getting rid of the inhomogeneous line. We consider an n-level atom (fig. 1) where two relevant levels a and b with the same pari ty can be coupled by two-photon processes via all the other intermediate levels of suitable pari ty to satisfy the selection rules for one-photon processes. We introduce an interaction with a classical field that we write in the slowly varying envelope approximation as

Deep-water acoustical analysis of stationary and moving broadband sound sources

Deep-water sound transmission from a moving source to a fixed receiver is studied, where the source emits a random broadband signal whose expected distribution is normal. A bilinear sound-speed profile is employed, the source is located above the SOFAR axis, and the receiver below. Long ranges are assumed, so that only SOFAR rays need be considered. Basic propagation equations are given, and travel time and spreading loss expressions are approximated in stability regions within which all four SOFAR rays exist for each number of SOFAR-axis crossings. General equations are derived for the received average power spectrum and power in terms of the spectrum at the source. Then, the broadband signal is taken to be bandlimited white noise. The received spectrum is simplified and examined for nonmultipath, multipath, and Doppler contributions. The influences of range, source speed, frequency, and observation time are considered. Average power at the receiver is studied similarly. Received spectra for a stationary source are investigated, and exhibit greater variations than those arising from a moving source. However, received average power for stationary and moving broadband sources are about equal. Average received power from cw and broadband sources, both moving and stationary, are compared. Power variations in the cw case are found to be much larger than in the broadband case.

Radiative transfer across expanding laser-produced plasmas. I. Line profiles

The transport of line radiation transverse to the axis of an axisymmetric expanding plasma, such as a laser-produced plasma, has been studied for line profiles in which the Doppler contribution from ion streaming varies from being negligible to being the dominant cause of line broadening. Emergent line profiles computed for model source functions and for profiles which are intrinsically Gaussian or Lorentzian illustrate the broad range of profiles which might be observed. Absorption by the plasma of radiation incident from outside is also considered. Astrophysical comparisons are made and a possible source of error in the wavelength determination of lines from a laser-produced plasma is pointed out.

An experimental study of the shapes of microwave spectral lines in gases at low pressures

A spectrometer which has been used for studying the shapes of microwave spectral lines in gases is described. Radiation from a klystron was passed through a waveguide cell and detected with a crystal diode. The klystron frequency was modulated sinusoidally with a frequency of f/n, n being integral and in the range 1 to 5, and the detected output at frequency f was observed on an oscilloscope. In this way the first five harmonics of the modulation frequency were observed. The mean klystron frequency was swept slowly across the spectral line and the frequency separations between the various maxima and minima of the harmonic outputs were measured using frequency markers. The results were compared with those deduced from three theoretical lineshape models. Three cases were studied; the self broadened (J,K)=(6,6) line in the inversion spectrum of NH3 the same line broadened by He; and the self broadened J=1 to 2 line in the rotational spectrum of COS. In all cases the lineshape was represented to within the experimental error by a Lorentz shape corrected for the Doppler contribution.

Doppler period variations of high-velocity pulsars

The effect of the source motion on the period variation of pulsars is investigated. For some pulsars, a velocity 100–300 km/s can give a Doppler contribution to the second period derivative P which is comparable or larger than the intrinsic variation predicted by theoretical models, whereas larger velocities are required in order to give an appreciable kinematic effect on the first derivative P. The possibility of experimental detection of P and proper motion for known pulsars is discussed.

Analysis of Debye-Waller—Factor and Mössbauer-Thermal-Shift Measurements. II. Thermal-Shift Data on Fe

Techniques developed in a previous paper are used to subtract the second-order Doppler contribution from measured thermal shifts on pure Fe and dilute Fe in various hosts. This allows the temperature dependence of the isomer shift arising from the electron density at the nucleus to be seen more clearly than was previously possible. It is shown that this temperature dependence cannot be accounted for by thermal expansion alone. In pure Fe a contribution related to the magnetization is clearly evident, as is theoretically expected. A contribution in addition to this and the thermal-expansion contribution is present, contrary to the conclusion generally drown from previous work. The additional contribution to the isomer shift is discussed in terms of two theories which have been used to explain the temperature dependence of hyperfine coupling constants.