Showing papers on "Doppler broadening published in 1973"

Optical Escape Factors for Bound-bound and Free-bound Radiation from Plasmas. I. Constant Source Function

Abstract: Optical escape factors for bound-bound and free-bound radiation have been calculated by solving the equation of radiative transfer with the assumption that the corresponding source functions are space-independent. The general expression for bound-bound transitions yields for large optical depths—within a correction factor of order unity—Holstein's asymptotic expressions for the two limiting cases of a Doppler and a dispersion profile. Application to the more general case of a Voigt profile leads to an analytical formula which permits a rapid estimate of the escape factor for any optical depth. Numerical application to the resonance lines of neutral helium-which are broadened by Stark and Doppler effects—shows that under certain plasma conditions most of the higher members of the resonance series remain optically thin.—The general expression obtained for the escape factor of free-bound radiation has been applied to the resonance continuum of neutral helium. The numerical results show that the resonance continuum remains optically thin as long as the optical depth in the center of the He resonance line (λ = 584 A) remains smaller than 104 to 105. A similar result is obtained for atomic hydrogen.

An approach to the theory of pressure broadening of spectral lines

Abstract: An attempt has been made to give a rigorous treatment of pressure or Stark broadening under the following assumptions: 1) the perturbating particles move independent of each other on straight lines with constant velocity v. The particles are distributed in the space with mean density n, the directions of their velocities are uniformly distributed on the unit sphere. 2) We neglect at all interactions of particles whose impact parameter is bigger than some constant ρ and we neglect interactions of particles with impact time tp at times t with |t − tp|⩾τ/2 where τ is another constant. Under these assumptions we get two formulae for the line profile I(ω) or its Fourier transform R(t)= = ∫ I(ω)eiωtd, Part II, Theorem 3 and 4. Both formulae are very similar in character. They consist of terms which are sums of one-particle-interactions, two-particle-interactions and so on. The first formula holds for any value of n, v, τ and ρ whereas the second one can only be proven for nπρ2 v τ < log 2. But the second formula is independent of τ and its one-particle approximation even of ρ. A detailed discussion of the second formula has been made in I. It clearly shows the nature of impact approximation.

Non-coherent scattering

Abstract: The paper is devoted to the consideration of the problems of non-coherent scattering in a spectral line for an arbitrary redistribution law. The representation of the redistribution function r(x′,x) in the form r(χ′,χ) = ∑ k = 1 ∞ A k α k (χ′)α k (χ) is used to study the various mechanisms of line broadening. The form of representation plays an important role in this investigation. New methods for solving radiative transfer integro—differential equations, as well as the corresponding integral equations are suggested. The solution of integral equations involves factorization of matrix integral operators. The generalized classical problems of absorption-line formation in stellar atmospheres are formulated and solved (Shuster's and Eddington's models). The results of numerical calculations, carried out to the fourth order, are given for Doppler broadening.

A Microwave Spectrometer with an Internal Glow Discharge

Abstract: A microwave spectrometer which utilizes the positive column of a dc glow discharge as its sample region has been constructed and operated successfully. This instrument employs free space microwave propagation through a large industrial Pyrex pipe, along with Zeeman modulation, and is intended for the study of transient paramagnetic molecules which are likely to be found in active discharges. This spectromenter features no mechanical tuning, instantaneous broad band width, resolution limited by Doppler broadening, and sensitivity comparable to that of conventional Stark modulated waveguide cells. Extensive observations primarily of the microwave spectrum of the OH radical in a water vapor discharge, have been made in order to delineate the range of application of this technique and to determine the effects of various operating parameters on the spectrum observed. Although the glow discharge is an extremely complicated phenomenon and is capable of manifesting its complexities in the behavior of our spectrom...

A theoretical study of the effects of ion motion on spectral lines in plasmas. I. Neutral helium lines

Abstract: A theory of spectral line broadening in plasmas which accounts for the ion dynamic broadening is reviewed and modifications are made to achieve a form which is amenable to calculation. The calculational procedure is discussed. The results are compared with other theories of spectral line broadening in plasmas and experimental data. A brief discussion is given of the alternative methods used to introduce ion dynamics into line broadening formalisms.

Spectral broadening of an acoustic pulse propagating through turbulence

Abstract: The following analysis develops the equation for the scattered acoustic power and spectral broadening of a plane acoustic pulse propagating through atmospheric turbulence that is moving with a uniform wind transverse to the beam. Assuming weak single scattering, the resulting propagation broadening is proportional to the wind velocity divided by the outer scale of turbulence and is independent of the strength of turbulence and total propagation range. Further, the broadening for a medium with variable outer scale and wind shear (e.g., a vertical propagation path) is determined primarily by the highest ratio of transverse wind to outer scale encountered by the pulse.

Study of the libration of the ammonium ion in ammonium bromide in the ordered tetragonal phase by Raman spectroscopy

Abstract: The frequency, intensity, spectral bandwidth, and the Raman polarizability correlation function associated with the librational motion of the NH4+ ion in NH4Br below Tλ has been studied in detail as a function of temperature by Raman spectroscopy From the second moment data, the earlier proposed reorientational mechanism was ruled out as a cause for the spectral broadening The correlation time and spectral linewidth versus temperature data both show an Arrhenius type of temperature dependence This temperature dependence was attributed to the thermally induced hydrogen bond breaking process

Effect of collisions on the random electron density fluctuations in a plasma

Abstract: The random fluctuation spectrum of the electron density is calculated by orbital statistics for arbitrary electron velocity distributions, and for a velocity dependent collision frequency nu . It is shown that collisions produce two effects: spectral broadening due to phase interruption, and spectral narrowing due to a reduction of the forward velocity by dynamical friction. For a Maxwellian velocity distribution all results are expressed in terms of the error function of complex argument and, for constant nu , they are practically equivalent to results obtained earlier from the autocorrelation function of a Brownian particle.

Laser Doppler instrument for measurement of vibration of moving turbine blades

Abstract: A laser Doppler instrument using a 1 mW laser has been developed for the measurement of the vibration of moving objects. Particular interest has been taken in rotating turbine blades. The design and optimisation of the instrument are described, and details given of its performance and resolution. It is shown that resolution is limited by signal/noise ratio and by Doppler broadening, both of which can be predicted. A coherence loss factor is established which enables the expected signal/noise ratio to be estimated from simple ‘noncoherent’ measurements of light scattered from a target. Experiments are described which compare the performance of photomultipliers and avalanche photodiodes. The instrument has been used successfully on a turbine having blade-tip velocities up to 300 m/s, equivalent to Doppler shifts up to 1000 MHz. At the lower frequencies, photomultipliers and avalanche photodiodes are comparable in performance, but at the top end of the range only the latter is satisfactory. Resolution in velocity of about one part in 104 is achieved with an output bandwidth of 1 kHz.

Homogeneous broadening in a 0.63 μm single mode He-Ne laser

Abstract: The expression for inversion density in a gas laser includes an additional term if one allows elastic and/or resonant collisions among the active atoms. This term is a function of the line parametersγ 1, andγ 2 and describes the effect of homogeneous broadening on the saturated gain profile. Measurements of these parameters show that the homogeneous broadening in a 0.63 μm He-Ne laser plays an important role.

Doppler broadening of OI 1304 Å multiplet in dissociative excitation of CO2 and O2

Abstract: Emission of the atomic oxygen triplet at 1304 A produced by electron impact on O2 and CO2 was passed through an absorption cell of thermal O(3P) at 300°K and peak optical depths near 2000. The transmission of the cell varied from 18% and 75%, depending on electron voltage, gas, and viewing angle. Interpretations of the Doppler broadening effect were made in terms of approximate linewidth, dissociation energy, and excited state symmetry.

Relativistic Electron-Beam Pumped uv Gas Lasers

Abstract: Stimulated emission occurs when (ortho- and para-) H2, HD, D2, CO, Ne, and N2 are excited by a 4-GW electron beam. The beam is generated by a Febetron, model 706, and propagates 2.3 m through the gases at 8–100-Torr pressures. Propagation is aided by an externally applied ∼ 10 kG magnetic field. Collisions involving primary, secondary, and cascade electrons transfer ≤ 0.1% of the energy from the electron beam to produce population inversions. The small-collision cross sections for relativistic electrons act as the primary limitation to the transfer of more energy to the gas molecules. Dependence of the laser energy on isotopes and temperature indicates that the spectral linewidth is due to Doppler broadening, and consequently higher power and optical gain are available by cooling the gases to ∼ 90 K or lower. The additional optical gain allows lasing to be observed at shorter wavelengths (1098 A as compared to 1161 A) and at higher powers near 1200 A (∼ 5 kW/ cm2 as compared to 0.5 kW/cm2) than reported p...

Broadening of the ESR line, caused by the variation of the cavity Q factor across the magnetic resonance

Abstract: The variation of the cavity Q factor across the magnetic resonance produces a broadening of the line when the number of spins is sufficiently large. The calculation of the maximum number of spins possible without broadening is given. With an amplitude modulated microwave field, a modification of the modulation ratio occurs, producing an additional broadening. The conditions which must be fulfilled if such an effect is to be prevented are given.

Ion temperature measurements in the range of 0.1-1 eV by means of the Doppler broadening of the 4686 AA He II line

Abstract: A method is described to determine the ion temperature in the range 0.1-1 eV from line profile measurements in a magnetized helium plasma of low density.

Structure of the H II regions M8 and M20. I. Kinematics

Abstract: A study of H alpha , STAN II!, and STAO III! line profiles was made in M8 and M20 using a Fabry-- Perot interferometer. Temperatures were estimated from both the relatlve widths and the relative intensities of H alpha and STAN II!. The two methods often showed large discrepancies. After removal of thermal Doppler broadening, the residual profile half-width was about 18 km s/sup -1/ for H alpha and STAN II!, and about 12 km s/sup -1/ for STAO III!. The observations did not verify the existence of expansion. (auth)

Ion temperatures in Ormak from Doppler broadening

Abstract: Rapid-scanning spectrometric techniques have permitted the determination of ion temperatures in ORMAK as a function of time during the discharge pulse for ORMAK plasma currents up to 180 kA Emission spectra of hydrogen atoms are Doppler-broadened in the line wings, characteristic of the initial proton motions prior to charge exchange, and give ion "temperatures" generally less than kT+ ~ 300 eV Impurity spectra of C III and O V, as well as the spectra of He II in helium discharges, lead to somewhat higher ion temperatures ranging up to a maximum of kT+ ~ 700 eV

Collisional broadening of the solar sodium D lines

Abstract: The center-limb variation of intensity in the wing of the solar, sodium D/sub 1/ line was analyzed to find the ratio of the line to continuum absorption coefficient as a function of wavelength shift and depth. The line absorption coefficiert varies as 1/ DELTA lambda /sup 2/, and, interpreting the variation with depth in terms of the Harvard Smithsonian Reference Atmosphere, the linear variation of the broadening parameter with density of hydrogen atoms is apparent. Using the recent calculations of broadening coefficients by Lewis et al. the abundance of sodium relative to hydrogen by number of atoms is (2.15 plus or minus 0.21 x 10/sup -6/. (auth)

Tunable-laser derivative spectroscopy on spectral lines with combined Doppler and collision broadening

Abstract: In derivative spectroscopy, we optimize the measurement sensitivity by utilizing the maximum excursion of the derivative of the spectral absorption coefficient as a single spectral line is scanned. Results for lines with pure Doppler or Lorentz contour have been given previously. We present here the required spectroscopic data for spectral lines with combined Doppler and collision broadening.

Stellar chromospheric velocity fields and the width luminosity relations

Abstract: The chromospheric width-luminosity relations observed for H alpha and the Ca Il and Mg II resonance lines are discussed. New electronographic observations of the H alpha line width in 33 late-type stars are presented and it is shown that these measures are consistent with the nonthermal broadening velocities deduced from the Ca II lines if thermal Doppler broadening with T/sub e/ ~ 6000 deg K for the hydrogen line is included. The differences in width between the Ca II and Mg II lines are interpreted in terms of the increase in nonthermal or microturbulent broadening velocity with height in a chromosphere. Both the magnitude and the ratio of these line widths in the Sun are sho~to be in good agreement with those expected from existing empirical and semi-empirical estimates of the acoustic energy flux neccssary to heat the chromosphere and corona. It is suggested that if suitable chromosphenic density scaling laws can be found, the width-luminosity relations provide a semi-empirical method of tracing the magnitude of the mechanical energy flux over the cooler part of the HR-diagram. (auth)

Stark broadening of Paschen lines in a deuterium discharge

Abstract: The Paschen lines P6 to P13 emitted from a radio-frequency discharge (Ne = 2.2 × 1013 cm-3) have been measured photoelectrically. The experimental profiles are compared with refined quasistatic calculations. These calculations include Doppler and apparatus broadening. It is shown that the quasistatic theory applied here provides a useful description of the line wings, as well as of the region around the halfwidth. Only at the line core must a contribution from electron collisional broadening be assumed to smooth structures retained in the quasistatic calculations. This contribution is small; its magnitude is estimated to be of the order of Griem's term accounting for strong collisions.

The influence of weak low frequency fluctuations in electron plasma wave experiments

Abstract: The various factors which lead to the spectral broadening of electrostatic plasma waves are discussed.

The influence of molecular blends and non-thermal line broadening on the profile of the Zeeman triplet λ5250.22 in sunspots

Abstract: Calculations of the umbral profile of the Zeeman triplet λ5250.22 are presented. We have taken into account the effect of a molecular blend from TiO at λ5250.24 causing an apparent π-component even for longitudinal magnetic fields. Also included is the depression of the spot continuum due to line wings and veiled weak lines in the umbra spectrum. The effect of different amounts of non-thermal broadening is investigated.

A band absorptance formulation for Doppler broadening.

Abstract: An expression is presented for the total band absorptance of vibration—rotation bands having Doppler-broadened lines. The result is similar in form to corresponding expressions for pressure broadening, in that the total band absorptance is expressed in terms of a dimensionless pressure path length, a bandwidth parameter, and a line-structure parameter. The band absorptance formulation is employed to estimate pressure levels at which Dopple broadening dominates over pressure broadening for CO2 bands within the atmospheres of Venus and Mars, and for CH4 bands within the atmospheres of Jupiter and Saturn.

Nonlinear effects in the emission and absorption spectra of gases in resonant optical fields

Abstract: The review systematizes the experimental material and reports the fundamental theoretical results on the study of nonlinear resonance effects in spectra of atomic systems situated in the radiation field of lasers. The theoretical part explains the topics of greatest importance and significance for understanding of the experimental studies: the Stark effect in an optical field; the nonequilibrium velocity distribution of the atoms; the shape of the spectral line for a transition adjacent to a transition combining with a strong field; the simultaneous manifestation of the Stark effect and of Doppler broadening in the form of a very sharp structure on the line contour; a brief mention of the influence of collisions, recoil, and other factors on the sharp structure in spectra. The experimental part reports the results of experiments on the observation of the Stark effect in the optical region of the spectrum, the fine structure of the profile of a Doppler-broadened line and its properties, namely the dependence on the observation direction, the anisotropy in the field of a standing wave, the polarization properties, etc. in spectra of spontaneous or stimulated emission, absorption, and generation.