Showing papers on "Doppler broadening published in 1987"
TL;DR: In this paper, the shape of the Balmer-α line emitted by a low-pressure rf 13.56 MHz discharge in hydrogen was analyzed using a monochromator with a high spectral resolution (0.04 A).
Abstract: The presented results are concerned with the shapes of the Balmer‐α line emitted by a low‐pressure rf 13.56‐MHz discharge in hydrogen. Optical emission analysis has been done using a monochromator with a high spectral resolution (0.04 A). Essentially, the lines present a central nearly Gaussian‐shape peak with a FWHM of about 0.3 A emerging from a wide pedestal constituted by two plateaus with widths equal to 0.9 and 1.5 A, respectively, and by large wings whose intensity quasilinearly decreases on both sides of the central wavelength. We explain these profiles by the Doppler broadening due to fast H atoms produced by the dissociative excitation and the dissociative ionization of the H2 molecules by electron impact generally followed by the excitation of the resulting atoms towards emitting states.
75 citations
TL;DR: In this article, the mesospheric temperature gradient of the D2 resonance line of atmospheric sodium excited by a laser and from the rotational distribution of the P1(1, P1, 3 and P1/4) lines of the OH(3,1) band was determined with an i.r. spectrometer at the Andoya Rocket Range.
61 citations
TL;DR: The annihilation characteristics of a monoenergetic beam of positrons, after implantation in Si with a 350nm overlayer of SiO2, were measured as a function of mean implantation depth as discussed by the authors.
Abstract: The annihilation characteristics of a monoenergetic beam of positrons, after implantation in Si with a 350‐nm overlayer of SiO2, were measured as a function of mean implantation depth. Positrons implanted overlapping the SiO2/Si interface were observed to decay from a state with properties distinctively different from the state in bulk Si and the thermally grown SiO2, i.e., a positron interface state. The momentum distribution of the annihilating positron‐electron pair, as observed in the Doppler broadening of the annihilation line, is much broader for this state than for either bulk Si or SiO2, in contrast to previously observed localized positron states in solids and at surfaces which show a narrower distribution.
59 citations
TL;DR: The induced spectral broadening about a weak non-phase-matched 530-nm second-harmonic pulse is observed by propagating an intense primary 1060-nm picosecond laser pulse through ZnSe crystals.
Abstract: The induced spectral broadening about a weak non-phase-matched 530-nm second-harmonic pulse is observed by propagating an intense primary 1060-nm picosecond laser pulse through ZnSe crystals. This broadening is attributed to the induced phase modulation of excitation states.
56 citations
TL;DR: The Doppler broadening of the two-photon annihilation line arising the intermediate lifetime of positronium in a magnetic field has been measured using a time selecting λ-ray spectrometer as discussed by the authors.
53 citations
TL;DR: In this article, a least-squares fitting parametric estimation for VHF Doppler spectra was proposed to determine the distribution and air motions of raindrop size distribution and vertical air velocity.
Abstract: Raindrop size distribution and vertical air velocity are directly derived from VHF Doppler radar spectra in precipitation environments. As was first proposed by Wakasugi et al., we use a least-squares fitting parametric estimation for VHF Doppler spectra to determine the distribution and air motions. After discussing further the VHF Doppler spectrum method, especially the effects of spectral broadening mechanisms, the method is applied to Doppler spectra obtained during the seasonal rain front (Bai-u front) observation in Japan. Variations of vertical air velocity and distribution parameters are discussed, based on this longer period dataset.
47 citations
TL;DR: In this paper, the authors demonstrate the existence of a spectral broadening effect in which VLF transmitter signals from Alpha station (geographic coordinates, 50.5{degree}N, 137°degree}E) in USSR undergo a significant spectrum broadening on electric fields as they propagate through the ionosphere up to the spacecraft in the altitude range of 500-2,000 km.
Abstract: Electric and magnetic field wave data acquired on Aureol 3 satellite demonstrate the existence of a spectral broadening effect in which VLF transmitter signals from Alpha station (geographic coordinates, 50.5{degree}N, 137{degree}E) in USSR undergo a significant spectral broadening on electric fields as they propagate through the ionosphere up to the spacecraft in the altitude range of 500-2,000 km at middle latitudes (L {approximately} 2). The spectral broadening phenomena may be divided into two types: (1) spectrally broadened components occurring without any association with ELF/VLF emissions under disturbed ionospheric conditions and (2) spectrally broadened components with predominant sideband structure in association with ELF emissions. Bicoherence computation results suggest a nonlinear mode coupling between the transmitter signal and ELF emission which produces sidebands that are quasi-electrostatic in nature. However, faint spectral broadened components in both types 1 and 2 may be connected with Doppler shift of quasi-electrostatic whistler mode waves with a broad spectrum of k near the resonance cone, due to scattering of the transmitter signals from ionospheric irregularities in the F region.
45 citations
TL;DR: It can be expected that water vapor retrieval will be possible with good accuracy even in the most critical cases, where steep gradients in aerosol backscattering exist in the upper troposphere.
Abstract: An evaluation scheme is given to calculate the water vapor content from data obtained by differential absorption lidar (DIAL), taking into account that the Rayleigh scattered part of the return signal shows considerable spectral broadening in contrast to the Mie scattered part. To correct for errors caused by this effect, information on the aerosol backscattering properties is necessary. Sensitivity analysis performed by model calculations show that it can be retrieved with sufficient accuracy from the off-line signal in the same way as for backscatter lidar. It can be expected that water vapor retrieval will be possible with good accuracy even in the most critical cases, where steep gradients in aerosol backscattering exist in the upper troposphere.
42 citations
TL;DR: In this article, the gamma ray fluxes induced by accelerator neutrons were investigated by irradiating thin targets with neutrons of energies from 14 MeV to 0.025 eV, and the ratio of epithermal to thermal neutron flux was determined to be 2.0, a value that is similar to that in the moon.
Abstract: Cosmic rays interact with the surface of a planetary body and produce a cascade of secondary particles, such as neutrons. Neutron-induced scattering and capture reactions play an important role in the production of discrete gamma ray lines that can be measured by a gamma ray spectrometer on board an orbiting spacecraft. These data can be used to determine the concentration of many elements in the surface of a planetary body, which enables us to recognize individual geological units and provides clues to the bulk composition and in turn the origin and evolution of the body. To investigate the gamma ray fluxes induced by accelerator neutrons, experiments were carried out by irradiating thin targets with neutrons of energies from 14 MeV to 0.025 eV. The neutron fluxes at target position were measured by foil activation techniques. The ratio of the epithermal to thermal neutron flux was determined to be 2.0, a value that is similar to that in the moon. Gamma rays in the energy range of 0.1 to 8 MeV emitted by the targets and the surrounding material were measured by a high-resolution germanium detector. Most of the gamma ray lines that are expected to be used for planetary gamma ray Spectroscopy were found in the recorded spectra. These spectra were unfolded, background was subtracted, and gamma ray attenuation corrections were made to obtain the corresponding gamma ray fluxes from the targets. The majority of gamma ray lines were narrow without noticeable Doppler broadening except for the very broad 4.4-MeV line of carbon and five asymmetric germanium lines produced by the detector itself. The agreement of measured gamma ray flux ratios with calculated flux ratios for neutron-capture reactions showed that thermal neutron data can be used for theoretical calculations of low-energy neutron-induced gamma ray fluxes. This study was a first step toward a more realistic simulation of cosmic-ray-induced gamma-ray production and it indicates the importance of accelerator irradiation experiments to future planetary missions.
23 citations
TL;DR: In this article, a Doppler-free Lamb dip detection technique was used to obtain high-resolution Lamb dip spectra of OD and SiCl radical, with a width of 1.5 MHz.
18 citations
TL;DR: In this article, the authors present a method for practical width calculation including temperature dependence, and introduce a new procedure for Doppler broadening function calculation, which provides evidence that practical width varies considerably with temperature.
TL;DR: The broadening of CO(2) rotation-vibration lines has been investigated in the 200-300 K temperature range and it is found that the temperature exponent is nearly independent of the rotational quantum number within the limits of experimental error.
Abstract: The broadening of CO(2) rotation-vibration lines has been investigated in the 200-300 K temperature range. From an analysis of four lines (|m| = 8, 15, 20, 30), it is found that the temperature exponent is nearly independent of the rotational quantum number within the limits of experimental error, for both self- and oxygen broadening. Average values n(1) = 0.86 for CO(2)-CO(2) and n(2) = 0.94 for C0(2)-0(2) have been obtained. Comparison is made with the results of the theoretical calculation based on the Robert-Bonamy model.
TL;DR: Pulses as short as 43 psec were generated by Brillouin backscattering at 248 nm in cyclohexane and measurements show that the process is accompanied by considerable spectral broadening of the reflected radiation.
Abstract: Pulses as short as 43 psec were generated by Brillouin backscattering at 248 nm in cyclohexane. The measurements show that the process is accompanied by considerable spectral broadening of the reflected radiation.
01 Jan 1987
TL;DR: In this paper, the authors show that for resonance frequencies v 0 in the rf regime, the narrowing of optical resonances by cooling to low temperatures, T, has obvious limits.
Abstract: The progress in atomic and molecular spectroscopy has gone hand in hand with improvements of the resolution. Before the tunable narrow-band lasers led to the invention of Doppler-free techniques, spectral lines from cooled hollow-cathode discharges(1) had typical widths larger than 300 MHz, and high resolution was achieved only in rf spectroscopy, e.g., within hyperfine structure multiplets, by the classical techniques like atomic beam magnetic resonance,(2) optical pumρing,(3) or double resonance.(4) While the Doppler broadening
$$\delta {v_D} = {v_0}{\left( {{{8kT{\rm{ }}\ln {\rm{ 2}}} \over {m{c^2}}}} \right)^{1/2}}$$
(1)
is negligible for resonance frequencies v 0 in the rf regime, the narrowing of optical resonances by cooling to low temperatures, T, has obvious limits. On the other hand, Eq. (1) holds for an isotropic thermal velocity distribution, and a narrow Doppler width requires a reduction in the spread of velocity components only along the direction of observation. It is well known from ion optics that this can be achieved by electrostatic acceleration.
TL;DR: In this article, the authors measured the hydrogen coverage on W(001) by using the resonant nuclear reaction 1H(15N, αγ)12C and found that the coverage was 1/50 of the full monolayer, i.e. 4×1013 H atoms/cm2.
Abstract: Hydrogen coverage on W(001) was measured by using the resonant nuclear reaction 1H(15N, αγ)12C. The detection limit of the hydrogen coverage was 1/50 of the full monolayer, i.e. 4×1013 H atoms/cm2. The coverage dependence of the sticking probability of hydrogen was estimated by considering the ion-stimulated desorption of hydrogen. The zero-point energy of the vibration of adsorbed hydrogen atoms in the direction perpedicular to the surface was obtained by the Doppler broadening of the resonance width as 64±16 meV.
TL;DR: In this paper, the authors measured the frequency spectra of femtosecond pulses and found that the product peak intensity times interaction length approaches 5 × 10 11 W/cm.
TL;DR: A real-time display of the SBI-curve on the spectrum analyser provides the means of securing optimal CW Doppler spectra by minimising the Sbi-curves during acquisition.
Abstract: In an experimental study the value of the spectral broadening index (SBI) in continuous-wave (CW) Doppler measurements has been evaluated. The minimum SBI-value per heart beat (i.e. during systole) was calculated from intraoperatively obtained near-field and far-field Doppler spectra of the infrarenal aorta of 10 dogs. Near-field Doppler spectra show the same shape as far-field Doppler spectra but have a significantly different SBI. The minimum SBI of CW Doppler only contains useful information if the Doppler measurements are performed in the far field using a wide ultrasound beam (low emitting frequency). In that case the velocity profile in the blood vessel can be deduced from the SBI. The SBI depends strongly on the distance between the main axis of the ultrasound beam and the centre of the insonated blood vessel. A proper centring of the ultrasound beam corresponds with SBI-curves during the heart cycle which shown minimal spectral broadening. A real-time display of the SBI-curve on the spectrum analyser provides the means of securing optimal CW Doppler spectra by minimising the SBI-curve during acquisition.
TL;DR: In this article, the influence of thermal averaging on the collisional broadening and shift parameters of spectral lines is analyzed in the framework of the adiabatic phaseshift theory under an assumption that Doppler broadening can be neglected.
Abstract: The influence of thermal averaging on the collisional broadening and shift parameters of spectral lines is analyzed in the framework of the adiabatic phaseshift theory under an assumption that Doppler broadening can be neglected. Temperature variations of the width and shift rates in a very wide range of temperatures are examined for two different forms of interatomic potentials. It is shown that for a Lennard-Jones potential the averaging over a Maxwellian distribution of velocities is necessary only at rather low temperatures. Calculations performed for a more complicated shape of the potential difference curve, having a double minimum separated by a barrier, indicate that in such a case the Maxwellian averaging can be very important even at high temperatures.
TL;DR: In this paper, a least-squares computer routine accounting for competing broadening contributions extracted the pressure broadening parameters from the raw data and compared the results of Cahuzac and Damaschini (1977), (1980) for the helium line and with those of Kuhn and Lewis (1967) and Jabr and Bennett (1980), for the neon line.
Abstract: Laser polarisation spectroscopy has been used to measure broadening and shift of the helium 587.6 nm and the neon 588.2 nm lines in a low-pressure glow discharge. A least-squares computer routine accounting for competing broadening contributions extracted the pressure broadening parameters from the raw data. The results are compared with those of Cahuzac and Damaschini (1977), (1980) for the helium line and with those of Kuhn and Lewis (1967) and Jabr and Bennett (1980) for the neon line.
TL;DR: A positron annihilation of Doppler broadening in crystalline, quasicrystalline and amorphous Al-Mn-Si alloys is presented in this article.
Abstract: A positron annihilation of Doppler broadening in crystalline, quasicrystalline and amorphous Al-Mn-Si alloys is presented. The density of trapping sites is found to be similar in the crystalline and quasicrystalline alloys but much greater in the amorphous alloy.
TL;DR: This work has compared high-resolution coherent anti-Stokes Raman spectroscopy measurements of the Q(1) transition of H(2) with theoretical line shapes incorporating both Doppler broadening and motional narrowing to find line shapes that agreed well with observed spectra.
Abstract: We have compared high-resolution coherent anti-Stokes Raman spectroscopy measurements of the Q(1) transition of H(2) with theoretical line shapes incorporating both Doppler broadening and motional narrowing. Least-squares fits varying the motional narrowing coefficient for both the hard- and soft-collision model yielded line shapes that agreed well with observed spectra at 295 K for pressures between 50 and 3050 Torr. However, the narrowing coefficient for the hard-collision model was pressure dependent, whereas the narrowing coefficient for the soft-collision model was independent of pressure and yielded an optical diffusion coefficient that agreed with previously measured values.
TL;DR: In this article, the existence of poloidal vortex motion in spheromaks produced in a conical theta pinch was revealed and the poloidal velocity on the axis was estimated to be 5 cm/μsec.
Abstract: Spatially resolved spectroscopic measurements revealed the existence of poloidal vortex motion in spheromaks produced in a conical theta pinch. The poloidal velocity on the axis was estimated to be 5 cm/μsec. Large Doppler broadening, which previously was inferred as high ion temperature, is attributed to large internal fluid velocity. A possible effect of the vortex motion in a spheromak merging experiment is studied and found to enhance the fusion reaction rate as a finite temperature beam collider.
TL;DR: In this article, the authors studied the non-LTE line transfer with convective transport of excited atoms and presented self-consistent solutions of the radiative transfer equation and the kinetic equation of the excited two-level atoms.
Abstract: This second part of our study of non-LTE line transfer with convective transport of excited atoms presents self-consistent solutions of the radiative transfer equation and the kinetic equation of the excited two-level atoms, for the limiting case of no elastic velocity-changing collisions of the excited atoms. Pure Doppler broadening of the spectral line is assumed. We investigate reflecting and destroying boundaries for the excited atoms, while the boundary condition for the photons corresponds to free photon escape from the system. Our numerical procedure for solving the two coupled kinetic equations for the excited atoms and the photons is an iterative method using variable Eddington factors, and is described in detail. We present a simple model that considers the gas of excited atoms and the radiation field as two interacting fluids, which yields a straightforward interpretation of the various scale lengths encountered in the numerical results for the hydrodynamic properties (density, flux density, mean velocity) of the gas of excited atoms.
TL;DR: Increased peak frequency and spectral broadening are the result of a stenosis greater than 30% cross-sectional area, based on results of in vitro steady flow experiments in straight tubes.
Abstract: Quantitative analysis of continuous wave (CW) Doppler spectra by measurements of peak frequency and spectra broadening is an important non-invasive method for detecting disturbed flow caused by carotid arterial stenosis. It is known that severe stenoses can be detected; however, the spectral changes associated with minor or moderate stenoses may not be detected or can potentially be confused with those produced by flow disturbances in the normal carotid bulb. In order to determine if the flow disturbances in a normal bulb and those associated with a minor stenosis produce significant spectral changes, Doppler spectra were recorded from straight tubes with bulbs or stenoses in an in vitro model with steady flow rates of 400, 600, and 800 cc/min (Reynolds numbers of 1700, 2600, and 3500). Stenoses greater than approximately 30% cross-sectional area were associated with an increased peak frequency and increased spectral broadening as measured by spectral broadening index (SBI), coefficient of variation (CV), coefficient of skewedness (CS) and coefficient of kurtosis (CK). Stenoses less than 30% were not detected. With flow rates of 400 and 600 cc/min, the presence of a bulb did not affect peak frequency or the extent of spectral broadening. With a higher flow rate (800 cc/min), there was an increase in SBI, CV and CS but no increase in peak frequency. Based on the results of these in vitro steady flow experiments in straight tubes, we conclude that increased peak frequency and spectral broadening are the results of a stenosis greater than 30% cross-sectional area. Bulbs and stenoses less than 30% do not produce significant changes in the continuous wave Doppler spectrum with flow rates in the clinical range.
TL;DR: In this paper, a confined alpha particle diagnostic using pellet injection is proposed, where the alpha particle density can be obtained from the number of decaying photons emitted from the radiative decay of He+* (n ≥ 2) ions produced through the one-electron transfer reaction of an alpha particle by a probing ion ablated from the pellet before it is fully ionized.
Abstract: A confined alpha particle diagnostic using pellet injection is proposed. The alpha particle density can be obtained from the number of decaying photons emitted from the radiative decay of He+* (n ≥ 2) ions produced through the one-electron transfer reaction of an alpha particle by a probing ion ablated from the pellet before it is fully ionized. The counting rate, estimated using theoretical cross-sections, and the calculated pellet ablation rate are sufficient for observation against the bremsstrahlung background. The alpha particle velocity distribution can also be obtained from the Doppler broadening of the emission lines.
TL;DR: It is shown that time-varying velocity produces frequency modulation of the backscattered signal in ultrasonic Doppler flowmeters for blood flow in the ascending aorta.
Abstract: It is shown that time-varying velocity produces frequency modulation of the backscattered signal in ultrasonic Doppler flowmeters. Further, for blood flow in the ascending aorta, it is estimated that the spectrum of the backscattered signal would have a very wide bandwidth in the acceleration phase.
TL;DR: The measurements confirm the existence of large deviations from calculated profiles that do not account for ion dynamical effects, and it has been found that a model to include ionynamical effects as a Gaussian broadening partly corrects the discrepancies.
Abstract: The line profiles of the Balmer ..cap alpha.. transitions of hydrogen and deuterium were measured simultaneously in a theta-discharge plasma. The characteristics of the light source were the following: peak electron density of the order of 7 x 10/sup 14/ cm/sup -3/, electron temperatures between 15 and 20 eV, and neutral and ion temperatures between 2.5 and 3.5 eV. The filling gas was helium with a 1% admixture of equal parts of hydrogen and deuterium. The experimental profiles were compared with a theoretical spectrum that was calculated taking into account the Stark broadening, independent Gaussian widths for each line, a fine-structure correction, and the instrumental broadening. In the data reduction a correction of the experimental data was made to allow for a radial inhomogeneity of the plasma. The measurements confirm the existence of large deviations from calculated profiles that do not account for ion dynamical effects. It has also been found that a model to include ion dynamical effects as a Gaussian broadening partly corrects the discrepancies. Finally, about 10% agreement is obtained when Lorentzian profiles based on relaxation theory calculations are used for the Stark broadening. Similar agreement is obtained with numerically simulated profiles.
TL;DR: The spectrum of the stimulated electronic Raman gain at 650 nm in Ne I, pumped by a 633-nm He-Ne cw laser in the same cavity, is derived and the question of the proper Raman-gain linewidth is addressed.
Abstract: The spectrum of the stimulated electronic Raman gain at 650 nm in Ne I, pumped by a 633-nm He–Ne cw laser in the same cavity, is derived. The question of the proper Raman-gain linewidth is addressed. It is shown that the gain has a nearly Doppler-free component whose width is measured as 30 ± 10 MHz (FWHM) at 6 Torr. This value agrees reasonably well with the residual Doppler broadening but not with collisional broadening rates. A simple calculation is included that shows the quantum-limited frequency uncertainty of the 650-nm laser to be higher by a factor of 1.5 than the frequency uncertainty of the 633-nm laser at equal power.
TL;DR: In this article, the impact of the atomic scale structure of the interfaces of AlInAs GaInAs quantum wells grown by atmospheric pressure metallorganic vapor phase epitaxy upon absorption and emission spectra is studied in detail.
01 Sep 1987-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the authors present new theoretical results for the characteristics and performance of an rf-linac-driven XUV free electron laser, which fall into two categories: (1) the dependence of the small-signal gain upon the transverse phase-space distribution of the electron beam and geometry of the optical resonator, and (2) the optical spectral bandwidth.
Abstract: We present new theoretical results for the characteristics and performance of an rf-linac-driven XUV free electron laser. These results fall into two categories: (1) the dependence of the small-signal gain upon the transverse phase-space distribution of the electron beam and the geometry of the optical resonator, and (2) the optical spectral bandwidth. Concerning (1) we discuss, and present 3-D numerical calculations of, the small-signal gains expected for different phase-space distributions. The gain also varies substantially with the Rayleigh range of the optical resonator. Thus, for maximum small-signal gain, the design of the resonator is coupled to the electron beam characteristics. Concerning (2), we discuss conditions under which there is a spectral broadening of the optical pulse due to the development of sidebands. The basis of these studies are 1-D finite pulse, and 3-D periodic boundary condition, numerical computer codes.