Showing papers on "Doppler broadening published in 1979"

Doppler-broadening measurements of x-ray lines for determination of the ion temperature in tokamak plasmas

Abstract: Ion-temperature results are deduced from Doppler-broadening measurements of the $K\ensuremath{\alpha}$ ($1s\ensuremath{-}2p$) resonance line emitted from heliumlike iron impurity ions in the hot central core of PLT (Princeton Large Torus) tokamak discharges. The measurements were performed using a high-resolution Bragg-crystal spectrometer with a multiwire proportional counter.

Line shape and Doppler broadening in resonant CARS and related nonlinear processes through a diagrammatic approach

Abstract: We examine the effect of electronic resonance enhancement on the line broadening for Coherent AntiStokes Raman Scattering (CARS) and related third-order non linear processes, in low pressure gases. These phenomena are analysed theoretically within the framework of a time-ordered diagrammatic representation of nonlinear polarizations. Diagrams facilitate the classification of the various physical processes and provide a way to readily derive all the susceptibility contributions. In CARS, the susceptibility terms which are Dopplerfree and thus prevail in the Doppler limit are different from those which dominate in the collision broadening regime. This causes important changes in the spectral content. On the contrary, the same terms are seen to dominate, in both regimes, in coherent Stokes Raman scattering or in stimulated Raman scattering. Typical line contours are displayed. The generalization to all nonlinear processes is outlined. LE JOURNAL DE PHYSIQUE TOME 40, SEPTEMBRE 1979, Classification Physics Abstracts 33.10 33.20F 33.35 33.70 33.80K 42.65C

A normal mode theory of acoustic Doppler effects in the oceanic waveguide

Abstract: This paper considers the problem of computing the acoustic field generated by a moving point source. In particular, the acoustic field is obtained in terms of the normal modes of a horizontally stratified ocean. The source motion is assumed to be uniform (unaccelerated), but is not restricted to a path radial to the receiver. The structure of the Fourier inversion integral is carefully analyzed and an evaluation is carried out by the method of stationary phase. The stationary phase point is explicitly computed as an expansion in powers of the ratio of the source speed to the mode group velocity. The resulting expression for the velocity potential is examined for Doppler effects for both instantaneous (modal) Doppler as well as Doppler determined by a finite bandwidth Fourier transform.

Intensities and N2 collision-broadening coefficients measured for selected H2O absorption lines between 715 and 732 nm

Abstract: Intensities and N2 collision-broadening coefficients are measured for 62 water vapor absorption lines between 715 and 732 nm potentially applicable to laser remote sensing of atmospheric water vapor. Absolute line strengths and widths were determined from spectra corrected for instrument resolution, air-path absorption and Lorentz and Doppler broadening for pure water vapor and water vapor-nitrogen mixtures in a multipass absorption cell with a base path length of 25 m (White cell). Line strengths are observed to range from 4 x 10 to the -25th to 4 x 10 to the -23rd kayser/molecule per sq cm, and collision broadening coefficients are found to be approximately equal to 0.1 kayser/atm.

Spectral broadening of pulsating Al x Ga 1-x As double heterostructure lasers

Abstract: The longitudinal mode spectrum of stripe geometry double heterostructure (DH) lasers exhibits a spectral broadening of ∼ 0.8 A when the laser emits pulsations. The broadening results from a chirp to longer wavelengths which occurs during the ∼ 0.4 ns long pulse. The chirp is due to an increase of the refractive index resulting from the reduction in the carrier concentration during the pulse. Both plasma and band to band interactions affect the index change with the latter mechanism giving the dominant contribution. A comparison of the wavelength shift obtained during the pulse with the current dependent shift of the longitudinal modes at currents well below threshold confirms that the change in carrier concentration is responsible for the chirp.

Submicron Particle Size Measurements in an Acetylene-Oxygen Flame

Abstract: Diffusion broadening spectroscopy has been used to make in situ size measurements of submicron aerosol particles in an acetylene-oxygen flame. Making use of the spectral broadening of scattered laser light due to random particle motion, this optical technique has been demonstrated to be suitable for application in unsteady high temperature environments of 2200 °K in flowing gases. Particle sizes were found to vary from 40 to 250 nm as the height above the burner varied from 0·5 to 3·0 cm. Little variation was found as a result of equivalence ratio changes from 2·5 to 5·0. Sizes measured from electron microscope photographs of soot particles collected from the flame show reasonable agreement with those determined from scattering measurements. A method to measure geometric mean diameter and standard deviation of the particle size distribution in a polydisperse aerosol is also presented, and experimental results described. Modifications necessary to account for polydispersity and noncontinuum flow e...

A study of hydrogen charging of nickel by positron Doppler broadening

Abstract: The cathodic charging of hydrogen into polycrystalline nickel has been studied by measurements of the Doppler energy shifts of gamma-rays emitted during positron annihilation in the samples. In general, the annihilation photopeak initially narrows with hydrogen charging, indicating an increase in defect density. The extent of this photopeak narrowing increases with the amount of cold work prior to hydrogen charging. A mechanism is proposed in which dissolved hydrogen (protons) migrate to dislocations introduced by cold work and subsequently form gaseous hydrogen molecules and/or nickel hydride particles which have enough pressure and/or lattice misfit, respectively, to produce structural damage in the form of new dislocations at those locations. The broadening of the Doppler peak following the initial narrowing is attributed to protons reducing the attractive potential between positrons and dislocations. The results show that positrons can be an effective tool with which to study hydrogen in solids.

Experimental Evidence for Compensation of Doppler Broadening by Light Shifts

Abstract: Velocity-dependent light shifts may be used to suppress the Doppler broadening of an atomic spectral line observed along a given direction. We present emission spectra of $^{20}\mathrm{Ne}$ demonstrating the existence of such an effect for an appreciable portion of the atoms. Various possible applications taking advantage of the high anisotropy of this effect are suggested.

XUV spectroscopic studies of a carbon laser produced plasma

Abstract: The space-resolved spectrum emitted by a polyethylene laser produced plasma in the range 20-300 AA has been analysed. Plasma parameters, i.e. electron temperature and density, relative ion populations and plasma dimensions, have been determined. A model that takes into account Stark and Doppler broadening, Doppler shift and optical opacity, reproduces numerically the observed profiles of the Lyman lines of C VI with good accuracy and explains their build-up within the plasma.

Broadening of the Lyman-α line of hydrogen by low-frequency electric fields in dense plasmas

Abstract: Using the quasistatic approximation as basis for the description of broadening by ion-produced fields and the impact approximation for electron-produced high-frequency fields, an analytic approximation procedure is developed and applied which allows for slow variations of the total field acting on a radiating atom. This low-frequency Stark broadening depends on the radiator velocity and is therefore correlated with the thermal Doppler broadening. The theory is extended to Lyman-$\ensuremath{\alpha}$ lines of hydrogenic ions.

Inhomogeneous Broadening Effects in cw Chemical Lasers

Abstract: : The effects of inhomogeneous broadening on the performance of cw chemical lasers are investigated. A simple two-level vibrational model and a Fabry-Perot resonator are assumed. Laser performance is found to depend on certain parameters. Numerical results are presented for a cw chemical laser with laminar diffusion and with a single longitudinal optical mode. The variation of differential number density and local lasing intensity with streamwise distance and the variation of net laser output power with tuning frequency are presented. The latter exhibits a Lamb dip near linee center, which is in agreement with experimental observations. Thus, in typical devices, inhomogeneous broadening effects become negligible for p or = O(10) Torr. These effects become important in single longitudinal model lasers operating in the regime p (Torr) or = O(1) and in lasers wherein the streamwise length of the resonator is short compared with the streamwise length of the positive gain region.

Line Formation in Microturbulent Magnetic Fields

Abstract: The formation of Zeeman lines in Gaussian microturbulent magnetic fields is considered assuming LTE. General formulae are derived for the local mean values of the transfer matrix elements. The cases of one-dimensional (longitudinal), isotropic, and two-dimensional (transversal) magnetic microturbulence are studied in some detail. Asymptotic formulae are given for small mean as well as for small microturbulent magnetic fields. Characteristic effects of magnetic microturbulence on the transfer coefficients are: (i) the broadening of the frequency contours, although only for the case of longitudinal Zeeman effect and longitudinal magnetic microturbulence this effect can be described analogous to Doppler broadening, (ii) the appearance of a pseudo-Zeeman structure for nonlongitudinal magnetic microturbulence, (iii) the reduction of maximal values of circular polarization, and (iv) the appearance of characteristic linear polarization effects due to the anisotropy of the magnetic microturbulence.

Broadening and collisional relaxation of the potassium 52P level perturbed by rare gases: comparison of quantal calculations to semiclassical and experimental results

Abstract: The broadening and shift constants of the K 404.4, 404.7 nm doublet and the depolarisation cross sections of the 52P level perturbed by the rare gases are studied. The broadening and shift by helium, argon, neon and xenon have been measured. Calculations of all the collisional cross sections by a purely quantal method have been performed for helium. A mixed quantum-semiclassical method has been used for argon and xenon. Comparisons of quantum and coupled semiclassical calculations for helium indicate marked quantum and trajectory effects below 10 au. However the broadening and shift results agree within a few per cent due to the small relative weight of the short impact parameters. Much larger discrepancies appear for the other cross sections (up to 70%). Except for neon, the experimental results for broadening and shift verify quite well the theoretical predictions especially for the broadening. In particular the different broadening of the two lines is generally well predicted.

High-resolution coherent stokes Raman spectroscopy of theν 1 andν 3 bands of methane

Abstract: Coherent Stokes Raman spectra of the ν1 and ν3 bands of CH4 have been recorded in mixing two pulsed lasers (ruby and dye) of very good spectral and spatial quality. The results show a resolution of about 0.010 cm−1 for a 10 Torr pressure, corresponding in great part to Doppler broadening.

Intensity fluctuations in a ring laser taking into consideration a spatial population-inversion grating

Abstract: The correlation functions of the intensity fluctuations are calculated by use of a linearization procedure for the equations of motion which include the coupling of the counter-rotating travelling waves of the ring laser in the cases of Doppler broadening, of homogeneous broadening with a self-induced population-inversion grating, and in intermediate cases. Depending on the strength of the mode competition various stable stationary solutions exist for the amplitudes. The transition between these stable states shows phenomena closely resembling phase transitions such as critical fluctuations, critical slowing down, etc. In particular, when the system passes from the state where both modes are above threshold to the state where one mode is below threshold, the negative cross-correlation of the fluctuations also becomes critical. In the case of the transient behaviour of the ring laser in the unstable region the time development of the amplitudes and the correlation functions are described in a short-time approximation.

AC Stark effect and fluorescence using modulated laser beams. I. Effect of laser fluctuations and arbitrary relaxation parameters

Abstract: The influence of relaxation parameters, as well as temporal fluctuations in the laser field on the modulation rate and phaseshift of the fluorescence from a two-level atom excited by a weakly modulated source is studied in detail. It is shown that, for intense resonant laser fields, the resonance in the modulation rate occurs at the modulation frequency Omega =2 due to the dynamical Stark splitting and has a width equal to 1/2(T1-1+T2-1). When temporal fluctuations of the exciting laser field are taken into account, the phaseshift of the scattered light is found to be strongly dependent on the bandwidth of the exciting source, as well as the frequency of modulation; hence experimental results on the determination of the lifetime by the phaseshift method have to be interpreted carefully. Numerical results for the modulation rates and phaseshift at different field strengths and various values of T1-1, T2-1, Delta laser bandwidth and Doppler broadening are presented.

Fine structure and spectral broadening of Balmer lines in laser-produced plasmas

Abstract: The profiles of the Balmer lines emitted in a laser-produced plasma by the ions B/sup +4/ to F/sup +8/ have been observed. For the Balmer-..cap alpha.. line the fine-structure components are broadened and partially merged by the Stark effect, the thermal Doppler broadening, and the motional Doppler shift. To these lines a simplified model for a expanding plasma, used previously for the analysis of the Lyman lines of the same ions, has been applied. The results are in very good agreement with the observations, showing the overall validity of the interpretation. The various broadening mechanisms have been unfolded and, in particular, for the range of electron densities considered here, a transition between the weak- and strong-field approximations for the Stark broadening is evident.

A laser Doppler velocimeter for surface velocity measurement

Abstract: The velocimeter described is intended for measuring given lengths of iron wire in a rolling mill. The device is based on the conventional local oscillator heterodyne mode. To prevent the disappearance of the Doppler signal caused by movements of the wire in a direction perpendicular to the wire and laser beam, a broadening of the beam by means of a cylindrical lens is also proposed. The maximum Doppler frequency of the system is about 50 MHz, and the corresponding surface velocity is 66 m s-1 at a measurement angle of 14 degrees .

A lineshape of the trapped particle in anharmonic potential

Abstract: The line of resonance absorption of an atom in a gas usually suffers Doppler broadening. It has been first shown that the particle trapped in an anharmonic potential emits a narrow line with no Doppler broadening.

Application of Multigrid Energy Analyzer to the Scrape-Off Layer Plasma in DIVA

Abstract: A multigrid energy analyzer was used to measure the ion temperature in the scrape-off layer of DIVA, where the plasma parameters were relatively high, i.e. electron and ion temperatures Te and Ti\lesssim60 eV; electron density ne\lesssim5×1012 cm-3; heat flux q\lesssim2 kW/cm2. It was found that to obtain the true ion temperature, the bias voltage VE of the entrance apertures of the analyzer must be chosen so as to satisfy the criterion e|VS-VP|Ti, where VS and VP are the plasma potentials before and after the entrance apertures, respectively. The data were consistent with those obtained by other methods, i.e. the Doppler broadening of impurity lines and the Katsumata probe (ion-sensitive probe).

Preparation, Cooling, and Spectroscopy of Single, Localized Ions

Abstract: Certainly the most desirable conditions of experiments, to which an atomic physicist could ever aspire under the viewpoint of clarity and simplicity, include the preparation of a single, well-localized atomic particle. The realization of this concept, which requires some kind of entropy reduction or “cooling” of the particle [1, 2], would dramatically simplify the interpretation of experiments, e.g. in quantum statistics, and in studies of collective interactions with electromagnetic fields. Moreover, spectroscopic investigations of that particle could particularly benefit from the absence of most spectral broadening mechanimus: Doppler effect of 1st and 2nd order, transit-time broadening, and collisional broadening are eliminated [3]. Since only natural broadening is left over, this concept permits the detection of optical lines of unprecedented sharpness, and it offers an approach towards the ultimate atomic time and length standard.

Spectral line parameters of the ν4sRR (8,3) transition of NH3 using a CO laser

Abstract: The close coincidence between the 13–12 P (8) CO laser line and sRR (8,3) transition in the ν4 band of NH3 is used to find the spectral parameters of the absorbing line by fitting the Doppler and Voigt shapes to the appropriate regions of the transmittance curves. The self‐broadening parameter (linewidth) is found to be (8.11±0.43) ×10−4 Torr−1 cm−1. The foreign gas broadening coefficient with respect to N2 is measured to be 5.28±.90. The frequency offset between the laser and the center of the transition is determined to be approximately half the full Doppler width. From the line strength measurement, δμ/δQ is found to be 6.3±1.8 esu, approximately 20% smaller than that derived in an earlier determination based on total band strength, rather than that of a single line as is done here. The difference may be due in part to the unavoidable inclusion in the earlier work of the overlapping 2ν2 band.

HF Doppler observations associated with spread F

Abstract: This paper discusses HF Doppler spectrum observations at mid-latitudes when spread F was observed on local ionograms. The data indicate that Doppler broadening is related to spread F (they both commence simultaneously). The results can be simulated by using different ionospheric models. Calculations show that a rippled contour can cause HF Doppler broadening and range spreading on ionograms if the structure is traveling horizontally. Although this mechanism can lead to HF Doppler broadening, scattering at 4.5 and 7.5 MHz in an anisotropic medium from near overhead can also explain the experimental results. The observation of aspect-sensitive scatter does, however, depend critically on the statistical description of the irregularity spectrum. It is suggested that an experiment designed to measure the Doppler shift as a function of zenith angle may enable some of the current ambiguities associated with spread F to be eliminated.

Formation of radio signal spectral lines in propagation through circumsolar plasma

Abstract: The available experimental data on spectral line broadening for monochromatic radio waves propagating in the circumsolar plasma indicate the presence within the spatial spectrum of plasma inhomogeneities of an internal turbulence scale, the effect of which manifests itself in the finite values of the moments of the energy density distribution over frequency and in normatization of the spectral line form in the strong signal scattering regime. Theoretical analysis of line broadening produced by moving inhomogeneities in the solar corona has established a relationship between the second and fourth moments of the spectrum and the turbulence characteristics, permitting determination of the radial profile of the internal inhomogeneity scale for a known velocity of motion. According to Venera 10 data, the internal turbulence scale of the circumsolar plasma is of the order of magnitude of several km at distances of 5–10 solar radii and increases sharply with radial distanee. The change in the value of the internal turbulence scale with distance is of the same type as the dependence of ionic gyroradius on distance to the sun. Analysis of spectral broadening of radio signals is an effective means of studying such characteristics of inhomogeneities in the circumsolar plasma as the form of the spatial spectrum, the intensity of inhomogeneities, their rate of motion, the internal turbulence scale, and the radial profiles of these quantities. Simultaneously, the peculiarities discovered in the behavior of the spatial spectrum of the inhomogeneities require the completion of a stricter analysis of line broadening with consideration of radial variation of both the internal and external turbulence scales, a process which may explain other peculiarities of the spectral broadening of radio signals in the moderate and intense scattering regimes.

Excitation of Transitions between Atomic or Molecular Energy Levels by Monochromatic Laser Radiation. III. Effect of Doppler Broadening when Phase-Destroying Collisions Predominate

Abstract: The treatment of transient excitation of transitions between two atomic or molecular energy levels by monochromatic laser radiation under conditions in which phase-destroying collisions predominate is treated by means of numerical and approximate analytical solutions of the equations giving the rate of change of a modified density matrix. The analytical solutions are then used to obtain the transient values of the population of the excited state when Doppler broadening is taken into account. Numerical calculations are carried out for the ratio $\gamma ^{\prime}/\gamma $ = 10, where $2\gamma $ is the damping constant for diagonal and $\gamma ^{\prime}$ for non-diagonal elements of the density matrix. This extends the treatment given in two previous papers for the situation when $\gamma ^{\prime}=\gamma $, corresponding to very low pressures for which phase-destroying collisions are relatively unimportant.