Showing papers on "Doppler broadening published in 1976"

Saturated absorption line shape: Calculation of the transit-time broadening by a perturbation approach

Abstract: We present a third-order perturbation calculation of line shapes in laser spectroscopy based on the density-matrix formalism. The new feature of this theory is the inclusion of the Gaussian spatial structure of the laser beams. We study the linewidth as a function of relaxation and transit times. A shift is found when the wave fronts are not flat. General line-shape formulas are given as well as approximate formulas valid in various domains.

Identification of Absorption Lines by Modulated Lower-Level Population: Spectrum of Na 2

Abstract: Molecular absorption lines from a common lower level are intensity modulated by chopped-laser saturation of another line from that level. Populations of some other levels are also modulated by subsequent fluorescence. Both types of modulated lines are free of Doppler broadening. Also, collisional depopulation modulates absorption from rotational levels near the laser-depleted level. In ${\mathrm{Na}}_{2}$, we have identified 113 lines. Analysis of the $A$ state by Kusch and Hessel is confirmed and extended.

Exact Doppler Broadening of Tabulated Cross Sections

Abstract: The SIGMA1 (σ1) kernel broadening method is presented to Doppler broaden to any required accuracy a cross section that is described by a table of values and linear-linear interpolation in energy-cr...

Pulse broadening caused by deviations from the optimal index profile

Abstract: The excess pulse broadening caused by deviations from the optimal index profile is analyzed for multimode optical fibers. First-order perturbation theory is used to evaluate the effects of arbitrary index perturbations having longitudinal spatial frequencies which are too low to cause mode coupling. A simplified expression is found for the excess pulse broadening in terms of a double integral over a weighting function. Weighting functions are evaluated and used to calculate the effects of two kinds of circularly symmetric perturbations, a Gaussian-shaped bump or dip in the index profile and an oscillating perturbation. These perturbations are found to affect the pulse broadening significantly according to the position and width of the bump and the transverse spatial frequency of the oscillating perturbation. The more narrow bumps and those located at larger core radii are found to have the greatest effect. For a typical multimode fiber, perturbations making 2–18 oscillations along the radius are found to cause significant increases in pulse broadening, while more rapid oscillations are found to have negligible effect. These results indicate the type and degree of index profile control required to keep the pulse broadening below a specified level.

Three-Photon Doppler-Free Spectroscopy: Experimental Evidence

Abstract: We report here the first experimental demonstration of Doppler-free three-photon spectroscopy. The Doppler broadening is eliminated by insuring that the sum of the momenta of the three photons simultaneously exchanged between the atom and the laser beams is equal to 0. This is accomplished by making a proper choice of the angles between the three exciting beams. The observation has been made on the sodium $3{S}_{\frac{1}{2}}\ensuremath{-}3{P}_{\frac{1}{2}}$ transition with absorption of two photons and induced emission of one.

Microwave FM-CW Doppler radar for boundary layer probing

Abstract: A microwave FM-CW radar can obtain the complete spectrum of radial velocities of both precipitation particles and refractive-index fluctuations in the optically clear air. Heretofore the extraction of the Doppler spectrum from this type of radar was believed to be a formidable, if not impossible, task. We have implemented a Doppler processing technique that uses a data acquisition system developed for pulsed Doppler radar. We present Doppler spectra obtained with a zenith-pointing FM-CW radar that demonstrate this new capability. In addition to the strong refractive-index layers observed by the FM-CW radar in the optically clear air, there is evidence that scattering from a background continuum of Cn² can be detected when a Doppler operating mode is employed.

Auger spectroscopy on heavy-ion-atom collisions. I. Kinematic effects and apparatus

Abstract: This is the first of a series of papers dealing with the spectroscopy of electrons from heavy-ion-atom collisions The paper presents a simple treatment of the Doppler effect comprising of not only line shift and broadening, but also of the effect on the angular distribution For line broadening, previous approximations are replaced by a more accurate, but still simple, expression The potential or Berry effect for fast autionization processes is discussed Owing to interaction with the Doppler effect, the Berry width vanishes under certain conditions The experimental conditions are outlined and illustrated by sample calculations

Stimulated Brillouin scattering of CO2 laser radiation from underdense plasma

Abstract: Results of detailed measurements undertaken to compare experiment and theory of stimulated Brillouin scattering of high‐intensity CO2 laser radiation from underdense hydrogen and helium plasmas are reported. Spectral measurements confirm the ion acoustic wave as responsible for the backscatter. Ion Landau damping and collisions both contribute to spectral broadening. The maximum linear scattering growth rate γk was determined experimentally to be 6×1011 sec−1 in good agreement with a theoretical value calculated from random‐phase wave scattering. The value derived assuming coherent‐wave interaction was 1011 sec−1 which is a factor of 2 greater than the corresponding theoretical prediction. Temporal characteristics and reflectivity of the backscattered radiation are discussed.

Lyman‐α absorption photometry at high pressure and atom density kinetic results for H recombination

Abstract: Atomic absorption and fluorescence spectrophotometry have been routinely used in kinetic investigations as probes of relative, rather than absolute, atom concentration. The calibration of a Lyman-α photometer for measurement of absolute hydrogen atom concentrations at levels [H] ι ≤ 1.8 × 1014 atoms/cm2 and total pressure of 1.5 torr He is described. The photometer is characterized in terms of a two-level emission source and an absorption region in which only Doppler broadening of the transition is considered. The modifications due to pressure broadening by high pressures (500 ≤ P ≤ 1500 torr) in the absorption region are discussed in detail. Application of the technique is reported for the recombination of hydrogen atoms in the presence of six nonreactive heat bath gases. Experiments were performed in a static reaction cell at pressures of 500–1500 torr of heat bath gas, and hydrogen atoms were produced by Hg (3P1) photosensitization of H2. The technique is critically evaluated and the mechanistic implications of the hydrogen atom recombination results are examined. The measured room temperature recombination rate constants in H2, He, Ne, Ar, Kr, and N2 are 8.5 ± 1.2, 6.9 ± 1.5, 5.9 ± 1.5, 8.0 ± 0.8, 10.2 ± 0.9, and 9.6 ± 1.4, respectively, where the units are 1033 cm6/molec2 · sec.

Structure of density fluctuations near the sun deduced from Pioneer-6 spectral broadening measurements.

Abstract: Spectral broadening of monochromatic radio waves by density fluctuations near the sun is analyzed using the parabolic equation method. Application of the analysis to the 1968 Pioneer-6 spectral broadening observations yields indirect measurements of the density spectrum within 14 solar radii of the sun. For spatial wavenumbers of at least 0.0084 inverse km, the three-dimensional density spectrum is found to be close to the Kolmogorov spectrum (power law with spectral index of 11/3) and is consistent with interplanetary-scintillation and in situ spacecraft measurements farther from the sun. The magnitude of the density spectrum increases, but its shape remains the same during 'solar events' marked by increases in bandwidth.

Two-photon spectroscopy. II. Effects of residual Doppler broadening

Abstract: For pt.I see ibid., vol.8, p.1795 (1975) where the theory of Doppler-free two-photon transitions was discussed for the case of one single laser frequency. Here, the effects of two different frequencies are considered. When the residual Doppler width of the two-photon transition is less than the natural linewidth, the previous results are essentially regained. For large residual Doppler shifts, the absorption profile is a power-broadened Lorentzian if the frequency of the probe field is larger than the frequency of the strong field. In the opposite case, the absorption peak splits because of the AC Stark effect. The high-intensity distortions are minimized when equal frequencies can be used. Power-dependent shifts do not ordinarily occur with a resonantly tuned intermediate level. Some modifications of the spectra are introduced by phase-disturbing collisions.

Complete redistribution in the transfer of resonance radiation

Abstract: The assumption of complete redistribution in frequency used in the theory of transport of resonance radiation, when Doppler broadening is important, is shown to predict the correct number densities in the excited levels at large optical depth. The line shape, however, is not a Doppler distribution in the wings but decreases like effects. (AIP)

Spectral line narrowing in a gas by atoms trapped in a standing light wave

Abstract: This paper presents results of a theoretical analysis of a new method for eliminating the Doppler broadening of spectral lines and the broadening by the transit time of atoms through a light beam. The atomic motion in a one-dimensional standing wave is studied and the conditions for translational-to-vibrational motion transformation are found. The variation in the Doppler contour by the trapping effect is investigated. It is illustrated, in particular, that the width of the narrow peak at the line centre depends mainly on the finite transit time of the atoms through the light beam. Next it is shown that, by accumulating slow atoms in a three-dimensional standing wave, it is possible, in principle, to observe narrow peaks with their widths determined only by the natural line width. The possibility of experimentally detecting of the phenomenon is discussed.

Influence of Doppler and 'Stark' effects on the shape of the autoionization peaks in electron energy spectra produced in ion-atom collisions. Application to He+ and He0 on He collisions

Abstract: A detailed study is given of the influence of the Doppler shift and broadening on the spectra of electrons ejected by autoionization in collisions between heavy particles. General formulae have been obtained which permit us to discuss the validity of results already published by other authors. These results have been applied to the spectra of electrons ejected in He+-He collisions at 15 keV. The variation of the width of the autoionization peaks against ejection angle is well explained by Doppler broadening. On the contrary, the shape of these peaks cannot be due to the Doppler effect but rather to the Stark effect which is also studied in various experimental cases; the authors have verified that the latter effect disappears in collisions between neutral particles for which symmetric peaks at 15 keV are obtained.

The Doppler effect in a reflecting system

Abstract: The Doppler shift is derived for light incident at any angle upon a perfectly reflecting mirror moving in any arbitrary direction. The resulting equations confirm that there should be no Doppler shift for light reflected from a transversely moving mirror. This result disproves several previous theoretical predictions.

Utilizing the resonance line absorption technique to determine the collisional broadening parameters of a diatomic molecule: No γ-bands as an example☆

Abstract: The combined Doppler and pressure-broadening parameter can be determined for electronic bands of diatomic molecules by comparing measured spectral transmission data from a narrow line emission source with the computed transmission using a radiative transfer model. The parameter a' (which is proportional to the ratio of collisional plus natural half-width to the Doppler half-width) generally obeys the relationship a' = C(p/T), where p is the pressure in atmospheres, T is the temperature in °K and C is a constant. Application to the 0,0 γ-band of NO was made, and the value of C was found to be 1200(±200) °K/atm. This value of C leads to a value for the optical diameter of NO for collisional broadening in the presence of nitrogen of 3.4±0.3A.

A comparison of foreign gas broadening and shift of neon and argon emission lines

Abstract: Foreign gas broadening and shift coefficients for Ne and Ar emission lines produced in a high pressure (0·5-2·0 atm) He discharge have been measured. The shift coefficients vary significantly for different transitions. This variation results from the differing excited state potentials for the He-Ne∗ and He-Ar∗ collision pairs, which must be included in any reasonable quantum-mechanical calculation of line shifts. Even the small differences in broadening coefficients demonstrate the inadequacy of calculation of broadening from equations based on the Lindholm(1)-Foley(2) theory of collision broadening.

Integrated source-specimen system for high-temperature positron annihilation experiments

Abstract: A technique to prepare metal specimens containing sealed positron sources which permit Doppler broadening and lifetime measurements up to high temperatures (close to the melting point in the investigated metals Cd, Au, Cu) is presented.

A comparison of self broadening and shift of helium, neon and argon emission lines

Abstract: Self broadening (van der Waals and resonance) and shift of Ne emission lines and van der Waals broadening and shift of He emission lines have been measured using a high pressure (0.5–3.0 atom), low current discharge. These results are compared with previous measurements in Ar and He to obtain a complete comparison of self broadening and shift of He, Ne and Ar emission lines. Oscillator strengths for the resonance transitions are obtained from the resonance broadening coefficients. The trend of the van der Waals broadening coefficients for the three noble gases is correctly predicted by a theory due to HINDMARSH et al.(4) in which a Lennard-Jones potential is used in the impact theory formalism. The measured line shifts cannot be accounted for by this theory and reflect the need for more accurate quantum mechanical calculations.

Spectroscopic measurements of the plasma temperature in the ZT−1 toroidal pinch

Abstract: The plasma temperature in the ZT‐1 toroidal pinch as been determined using spectral line Doppler broadening measurements facilitated by the use of analog‐to‐digital converters and an on‐line computer. The ZT‐1 system has been operated in a ’’derated’’ mode with peak toroidal currents of 30 to 110 kA, initial current rise times of 0.5 to 2.5×1011 A/sec, stabilizing toroidal magnetic fields of 0.06 to 0.3 T, and filling pressures of 2 to 30 Pa. Results of the plasma temperature measurements in this mode of operation are reviewed with the objective of determining the effects of scaling the machine parameters on the ion temperature with extension to results obtained in the earlier higher current ’’fast’’ mode operation. An analysis and experimental tests of several possible sources of error in the ion temperature measurements are given in an appendix.

Abnormal broadening of boron emission lines in glow-discharge lamps: evidence for excitation in low-energy B-Ar(Kr or Xe) collisions

Abstract: The profiles of the boron resonance lines emitted from hollow-cathode and planar-cathode glow-discharge lamps have been studied for a variety of discharge conditions. For discharges operated in argon, krypton or xenon, the lines are extremely broad (halfwidths 0.13-0.27 AA) and are emitted very close to the cathode surface with unusually high intensity. The abnormal linewidths are due to Doppler broadening, which is unusually large because of a preferred excitation for those sputtered boron atoms possessing high kinetic energies of ejection. Investigations of the excitation process suggest that the energetic boron atoms are excited by inelastic collisions with rare-gas atoms. The high excitation efficiency at relatively low collision energies is interpreted in terms of curve crossings, which appear to be particularly favourable for some boron-rare-gas systems.

The temperature dependence of positron lifetimes in cadmium

Abstract: Positron lifetime studies in cadmium disclose a pattern of temperature dependence similar to that previously found in angular correlation and Doppler broadening studies. A value of 0.47+or-0.03 eV for the monovacancy formation energy is deduced.

Complex Doppler effect in dispersive media

Abstract: A one‐to‐one correspondence is demonstrated for Doppler shifted frequencies measured in different inertial reference frames. This result is reconciled with frequency splitting encountered in the complex Doppler effect. The analysis emphasizes the concept that it is not always sufficient to describe the Doppler effect for plane waves in homogeneous, isotropic, dispersive media by using only the conventional frequency equation ω=γ (ω′+v⋅k′). These ideas are illustrated in detail for the case of the cold plasma where the extra Doppler frequencies are given specific physical interpretations.