Showing papers on "Doppler broadening published in 1971"

Doppler Broadening in Beam Experiments

Abstract: The distribution in center‐of‐mass energy caused by the thermal motion of the target gas molecules has been rigorously derived for the case of a monoenergetic particle beam interacting with target molecules having an isotropic Maxwellian velocity distribution corresponding to temperature T°K. Provided the nominal c.m. energy E0 exceeds a few kT, the distribution has a full width at half‐maximum (FWHM) of W1/2=(11.1γk T E0)1/2. where γ=m/(m+M), m and M being the projectile and target masses. This is identical to the width derived previously in a one‐dimensional approximate treatment by Bethe and Placzek. The exact and approximate distributions differ significantly, however, in shape and mean energy, particularly at low values of E0/γkT. The Doppler width, W1/2, is shown to significantly affect the appearance curve of the products of endothermic reactions involving heavy particles. Convolution integrals are derived for a number of idealized forms of the cross section for such reactions. In the extreme case ...

A technique for recovering Doppler line profiles from fabry-perot interferometer fringes of very low intensity.

Abstract: A technique for recovering doppler line profiles from Fabry-Perot interferometer fringes of very low intensity is described. The technique is based on a fourier decomposition of the data and a subsequent nonlinear least squares fit of the low order fourier coefficients to the fourier decomposition of an ideal instrument function. The ideal instrument function is expressed by the convolution of various instrument broadening functions and includes a parametric representation of the actual instrument. The method for recovering doppler temperature, emission line intensity, and mass motion of the emitting molecules is described. A theoretical analysis of errors for doppler temperature and emission line intensity is made for a statistical noise distribution superimposed upon a fringe profile of very low intensity. These errors are related to the emission line intensity, number of data points per fringe, background continuum level, and instrument parameters. As a specific example, the errors in retrieving the doppler temperature from the 6300-A atomic oxygen emission line OI((1)D - (3)P) in the nightglow are determined for the 15-cm Fabry-Perot interferometer at the University of Michigan Airglow Observatory.

Reduction of Doppler broadening of spectral lines in fast-beam spectroscopy

Abstract: We show that the Doppler broadening, which arises in a fast‐beam light source because of the high speed of the emitters and the nonzero acceptance angle of the spectrometer, can often be practically eliminated by proper adjustment of the spectrometer.

Collision-broadened half-widths and shapes of methane lines

Abstract: High-resolution measurements are reported on a few rotational lines in the ν3-fundamental and the 2ν3-overtone of methane. Half-width data are presented in self-broadening and in broadening by H2, He, N2, O2 and air. Comparison with available data on 3ν3-band shows, within experimental error, that the line-widths are the same for ν3 and its overtones in all cases of broadening. The half-widths exhibit an observable dependence on the rotational quantum number only in self-broadening and nitrogen-(and air-) broadening. Line-shape measurements in the ν3-fundamental suggest that the Lorentz contour for collision-broadened lines in an accurate representation for all cases of broadening that were studied.

Measurement of Temperature and Aerosol to Molecule Ratio in the Troposphere by Optical Radar

Abstract: WE wish to describe preliminary optical radar measurements of atmospheric temperature and aerosol to molecule ratio. Optical radar can radiate pulses of highly monochromatic laser light and resolve the frequency spectrum of the light backscattered by atmospheric constituents. Because of the varying amounts of Doppler broadening which affect the spectra of the echoes from aerosols and molecules, it is possible to distinguish the contributions of the two species to the scattering cross section of a volume of air and infer their relative concentration.

Flow Properties of a Partially Ionized Free Jet Expansion

Abstract: Diagnostic studies were carried out in an induction‐heated low‐density supersonic plasma jet. The neutral number densities were obtained from the calibrated intensity of the 4609‐A argon II line excited by a 25‐kV electron beam, and the velocities and heavy particle temperatures were determined by measuring the Doppler shift and Doppler broadening with a Fabry‐Perot interferometer in two linearly independent directions, following a technique developed by Muntz. The contribution to the 4609‐A line due to the plasma self‐emission was found to be negligible. The density, impact pressure, and velocity along the free jet center line all followed the isentropic source flow model up to the Mach disc. The temperature, however, showed an unexpected rise above the isentropic prediction. Ion number densities and electron temperatures were measured with a double Langmuir probe. The fraction of ionization was frozen at about 0.1% along the free jet axis. Calculations of the fraction of the energy of recombination absorbed by the electrons and the fraction lost by radiation from an electron energy balance showed good agreement with an a priori estimate based on collisional‐radiative recombination.

Topics in Plasma Diagnostics

Abstract: 1. Oscilloscope Measurements of Current and Voltage in Pulsed Thermonuclear Devicesr.- References.- 2. Plasma Diagnostics with Probes.- 2.1. Langmuir Probes.- 2.2. Electrostatic Plasma Analyzer.- 2.3. Magnetic Probes and Pressure Balance.- References.- 3. Determination of Electron Temperature from Emission Intensity Ratios in Line Spectra.- 3.1. Line Spectrum of a Plasma.- 3.2. Low-Density Plasma.- 3.3. High-Density Plasma.- 3.4. Ionization State of a Plasma.- References.- 4. Determination of Plasma Parameters from the Shape of Spectral Lines.- 4.1. Introduction.- 4.2. Determination of Ion Temperature from the Doppler Broadening of Spectral Lines.- 4.3. Doppler Effect in a Scattered Light.- 4.4. Stark Broadening of Spectral Lines in a Plasma.- 4.5. Time Scan of a Spectral Line.- References.- 5. Continuous Spectra. Determination of Electron Density and Temperature.- 5.1. Brems Strahlung and Recombination Radiation in the X-Ray, Ultraviolet, and Visible Regions of the Spectrum.- 5.2. Infrared Region of a Continuous Spectrum.- References.- 6. Time Sweep Photography.- References.- 7. Determination of the Dielectric Constant of a Plasma.- 7.1. Measurement of Plasma Density with Microwaves.- 7.2. Interferometer Methods for Investigating Plasma in the Visible Region. Use of Lasers.- References.- 8. Particle Methods for Plasma Diagnostics.- 8.1. Use of a Beam of Charged Particles to Measure Electric Fields in a Plasma.- 8.2. Measurement of the Density of Neutral Particles and Charged Particles.- 8.3. Mass Spectrometer Method for Studying Fast Particles in a Plasma.- 8.4. Calorimetric Methods of Plasma Diagnostics.- 8.5. Detection of Hard Plasma Radiation.- References.- 9. Measurement of the Parameters of Accelerated Plasmoids.- References.

Cancellation of slit‐width and doppler broadening effects in the spectroscopy of fast ion beams

Abstract: We use the Doppler shift of light emitted by fast ion beams to cancel the broadening introduced by opening the spectrometer entrance slit Hence, wide slits are used to increase collected flux with minimal increase in recorded linewidth

Collision Broadening of Rotational Absorption Lines. VI. Pressure Broadening of Microwave Absorption Spectra Involving Oxygen

Abstract: The pressure broadening of microwave absorption lines by collisions involving O2 has been investigated using a method presented earlier for analyzing and evaluating microwave linewidth parameters under conditions where impact‐theory assumptions are valid. A value of (1.16 ± 0.12) D· A was obtained for the molecular quadrupole moment of O2 from linewidth data for broadening of NH3 inversion lines by O2. This value is in reasonably good agreement with values determined by other methods, and should constitute an upper limit to the true value since only dipole–quadrupole interaction was considered in the linewidth calculations, This value of the molecular quadrupole moment of O2 was used to calculate linewidth parameters for H2O–O2 broadening, OCS–O2 broadening, N2O–O2 broadening, O2–O2 self‐broadening, and the broadening of the 9– line of O2 by various foreign gases. These results are in general smaller than the experimental values, suggesting that the effects of higher‐order interactions are important in co...

Resonance broadening in the spectrum of potassium

Abstract: The self broadening of three doublets in the spectrum of potassium at low densities was investigated in emission from weak dc and rf discharges. The use of a double recording Fabry-Perot interferometer allowed an accurate measurement of the ratio of the broadening constants of the doublet resonance levels to be made. The value obtained 1.54+or-0.09, is in good agreement with recent calculations. The absolute values of the broadening constants are less accurate owing to experimental uncertainties in the vapour density but do not differ significantly from the theoretical values. The effects of nonresonance interactions on the broadening and shift are discussed.

Phase-locking millimetre-wave klystrons for the measurement of submillimetre laser frequencies

Abstract: A single-loop method of phase locking up to 100 GHz is described. Spectral broadening observed in harmonic mixing with an HCN laser at 891 GHz (with resolution 1 in 108) is attributed to phase noise and modulation on the base-reference quartz-crystal oscillator. Zero beats at 99 GHz between klystrons phase-locked to a common reference give frequency resolution of the order of 1 in 1013.

Quasi-Elastic Light Scattering from Solutions of Macromolecules. III. Detectability of Internal Modes of Motion

Abstract: The technique of quasielastic scattering of laser light is now becoming a powerful tool for the study of dynamic nature of biological macromolecules in solution. In the case of very large molecules, intramolecular micro-Brownian motion can be detected by the measurement of the Doppler broadening of scattered light. Without detailed calculation of the scattering form factors, it is discussed in this paper that under what experimental conditions it is possible to detect the internal modes of motion of macromolecules.

Application of a laser Doppler technique to the measurement of vibrations on moving objects

Abstract: A Laser Doppler Instrument has been developed for the measurement of vibrations on moving objects A particular interest has been taken in rotating turbine blades The technique used is similar to the well-known microwave Doppler radar system, but the many elements in an optical counterpart have been investigated The analysis of the coupling network between photodetector and following amplifier, and the optimization of the optical receiver para-meters such as beam splitting and current gain are amongst the main subjects of this work The signal and noise performance has been fully specified by means of a newly proposed Generalized System Noise Figure, Fs*, which is expressible as a function of a few simple, measurable parameters Using this Noise Figure a comparison between different systems and photodetectors such as photomultiplier, p-i-n and avalanche photodiodes, has been carried out and in conclusion the avalanche photodiode is recommended The minimum measurable vibration velocity depends on the Doppler broadening, and the optimum optical arrangement is calculated to minimize this effect Very closely related to the main work is the analysis of the performance of an avalanche photodiode used as an electronic mixer The results of measurements in the laboratory prove that it is feasible to measure vibrations on moving objects using laser Doppler techniques and that the analysis developed satisfactorily describes the performance of the system

Laser absorption measurement of electron temperature in an argon plasma.

Abstract: The electron temperature of an argon plasma created in an inverse pinch has been measured by the absorption of argon-ion laser light. The electron density, which is a necessary auxiliary measurement, can be determined easily with an interferometer whenever it is possible to measure the absorption coefficient. Then the electron density and the absorption coefficient provide sufficient information to determine the electron temperature with good accuracy, even when complete local thermodynamic equilibrium is not valid, and when Doppler broadening is important. The various parameters of the argon ion which are necessary for the calculation are tabulated.

Calculation of spectral line profiles for combined Doppler and Lorentz broadening

Abstract: The spectral profile of an isolated absorption line is related to the plasma dispersion function and/or the complex error function. A simple method for computing such profiles is given. The results can also be applied to calculation of the spectral profile emitted by a lamp.

Frequency Broadening in Reference Beam Laser Doppler Velocimeter Data

Abstract: : The laser Doppler velocimeter (LDV) provides velocity data in the form of a frequency spectrum. Because of the inherent optical geometry of the laser velocimeter and the effects of light scattering particles passing through the probe volume, a frequency distribution density function representing these combined effects is found in the readout device. Hence, interpretation of data must be effected for frequency-to-velocity conversion. This report deals with this frequency broadening effect associated with the LDV reference beam type. Six frequency broadening effects are discussed in terms of their magnitude and relative importance.

Signal broadening in the laser Doppler velocimeter.

Abstract: Critical review of a recent paper in which Denison, Stevenson, and Fox (1971) discussed the sources of spectral broadening in the laser Doppler velocimeter. It is pointed out that, in their discussion, the above-mentioned authors indicated that the spread in wave vectors of the incident and detected fields and the finite length of time a scattering center stayed in the sample volume each contributed separately and independently to the observed spectral width of the scattered radiation. This statement is termed incorrect, and it is shown that the two effects are one and the same.

Geschwindigkeitsverteilung anisotroper Deuteriumplasmen aus zeitaufgelösten Neutronenspektren

Abstract: The ion energy in hot deuterium plasmas can be determined by using the Doppler broadening of thed-d-neutron line at 2.45 MeV. A method allowing time resolved measurement of neutron spectra in pulsed discharges is described. It utilizes the known energy dependence of the total neutron cross section of light to medium weight nuclei for energy selection of the neutrons. The neutrons are detected with plastic scintillators which afford both a high detection efficiency and a time resolution in the nanosecond range.