Showing papers on "Doppler broadening published in 1975"
TL;DR: In this article, it was shown that a low-density gas can be cooled by illuminating it with intense, quasi-monochromatic light confined to the lower-frequency half of a resonance line's Doppler width.
1,039 citations
TL;DR: In this paper, a class of molecular two-photon processes, occurring under transient or steady-state conditions, is analyzed exactly for certain cases using a density-matrix formalism.
Abstract: A class of molecular two-photon processes, occurring under transient or steady-state conditions, is analyzed exactly for certain cases using a density-matrix formalism. Our results are relevant to the recently observed phenomena of transient coherent Raman beats and steady-state two-photon absorption of oppositely directed laser beams. Lowest-order perturbation theories have shown that these processes are insensitive to the Doppler effect, and consequently the linewidth is unaffected by Doppler broadening and by elastic collisions that change molecular velocity. The solutions presented here are of the same form for the Raman and two-photon problems and reveal significant power-dependent frequency shifts and line broadening that correct the ideal Doppler-free solutions. For the transient case, we assume a molecular three-level quantum structure that can be switched in or out of optical resonance with cw laser radiation by means of a pulsed dc Stark field, but the solutions also apply when resonant optical pulses are introduced. During the resonant condition when the Stark pulse is on, the three levels are prepared in coherent superposition, and during the nonresonant condition following the Stark pulse, the laser field(s) stimulates the coherently prepared sample in a transient two-photon process. One of these processes, the Ramanbeat effect, has been observed in forward scattering, but the second one, transient two-photon emission, should be observable in backward scattering. Bloch-like equations are derived for this three-level problem that facilitate an exact pulse solution for state preparation. Following the pulse, transient decay is well-approximated by a perturbation calculation. For the steady-state case, an exact solution is also obtained and is of interest for continuous-wave spectroscopy or for transient experiments requiring an initial preparation of quantum states, prior to Stark switching. These solutions exhibit a power-dependent line broadening and a frequency shift of magnitude $\ensuremath{\sim}\frac{\ensuremath{\Delta}({\ensuremath{\alpha}}^{2}\ensuremath{-}{\ensuremath{\beta}}^{2})}{({\ensuremath{\Delta}}^{2}+\frac{1}{{T}_{2}^{2}})}$, in agreement with our earlier estimate, where $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ are the Rabi flopping frequencies for the two intermediate transitions and $\ensuremath{\Delta}$ is the off-resonance tuning behavior for one of them.
215 citations
TL;DR: The High Frequency Deflection (HFD) technique is a further refinement of the conventional multichannel delayed coincidence technique with periodic electron excitation of free molecules as discussed by the authors, which is used for lifetime measurements in all kinds of atoms, molecules, ions and ion-molecules.
Abstract: The basic principles of the High Frequency Deflection (HFD) technique for the determination of atomic and molecular lifetimes as well as the first experimental tests were presented a couple of years ago In principle this technique is a further refinement of the conventional multichannel delayed coincidence technique with periodic electron excitation of free molecules The differences are mainly that the HFD technique utilizes a continuous electron beam from a high-power gun operating in the kilovolt range and that the periodic excitation is accomplished by sweeping the beam at an optimal rate, ie with a period equal to 3-10 times the lifetime to be studied With these two refinements the HFD technique enables lifetime measurements in all kinds of atoms, molecules, ions and ion-molecules with several orders of magnitude higher efficiency than other methods permit, thus opening possibilities for high resolution work in the absence of Doppler broadening Thus a number of lifetimes have been determined at a spectral resolution of 01 A FWHM or better, which is 20-50 times higher a resolution than what is normally achieved in lifetime measurements The variable sweep frequency and the multichannel registration make possible measurements over a large lifetime range (up to about 104 ns) which in turn offers unique possibilities for analysing multi-exponential decay curves With a time scale of arbitrary precision given by the sweep frequency, lifetime measurements have so far been performed with a total error down to 05% in favourable cases The HFD technique is now currently in use at this laboratory and several hundreds of lifetimes have been studied and reported in a number of publications In this paper we shall discuss more in detail the technique itself, its properties and possibilities compared to other methods for lifetime measurements A review of some of the experimental results obtained so far, with particular emphasis on abundance determinations of atoms and molecules of fundamental astrophysical interest, is also included as well as a critical discussion of given error limits in lifetime measurements in general
86 citations
TL;DR: In this paper, power broadening due to triple-quantum and higher multiplequantum transitions has been applied to the observation of the dynamic Stark effect by a direct splitting in the electronic Raman-Stokes contribution which occurs because of the partial compensation of the Doppler broadening.
Abstract: Cross-saturated absorption at the neon line 2s
2–2p
4 caused by the saturating line 3s
2–2p
4 has been applied to the observation of the dynamic Stark effect by 1) power broadening, due to triple-quantum and higher multiple-quantum transitions, of the light shift contribution to the susceptibility, and 2) a direct splitting in the electronic Raman-Stokes contribution which occurs because of the partial compensation of the Doppler broadening.
44 citations
TL;DR: In this article, the narrow line emission observed by Personov et al. at low temperature in a glassy matrix from perylene has been shown to be observable from many other molecules.
40 citations
TL;DR: In this paper, the authors show that as the Doppler broadening decreases, they saturate one another by scattering off induced Bragg gratings in the medium, i.e., off spatial holes burned into the population difference.
Abstract: Oppositely directed running waves in a ring laser saturate themselves and one another by population depletion. In addition, as the Doppler broadening decreases, they saturate one another by scattering off induced Bragg gratings in the medium, i.e., off spatial holes burned into the population difference. This increased coupling results in bistable operation near the atomic line center for Doppler-broadened media and for any equal tuning for stationary atoms.
27 citations
TL;DR: The influence of doppler broadening selector and analyser broadening, and stray field broadening on the observed widths of lines in different types of low energy electron scattering experiments are discussed in this article.
Abstract: The influence of doppler broadening selector and analyser broadening, and stray field broadening on the observed widths of lines in different types of low energy electron scattering experiments are discussed.
26 citations
TL;DR: In this article, the authors measured the spectral broadening of 1.06 μ pulses in KBr crystal and used the electronic Kerr effects and avalanche ionization to interpret the broadening and its upper limit at the Stokes side.
24 citations
TL;DR: In this paper, the authors considered the small-signal regime of a swept-gain amplifier with small Doppler width and found spectral broadening, saturation, and the formation of steady states.
Abstract: The buildup of radiation from noise is considered in the case of the small-signal regime of a swept-gain amplifier with small Doppler width, of the sort indicated in recent schemes for an x-ray laser. The treatment uses the fully quantized electromagnetic field in order to take into account the spontaneous emission. The pulse is seen to grow nonexponentially with a rate that vanishes in the limit of large distances. The gain is generally much smaller than would be expected on the basis of the usual development. Many of the features normally associated with the small-signal regime of an amplifier, such as threshold conditions and spectral narrowing, are not seen. Instead we find spectral broadening, saturation, and the formation of steady states.
TL;DR: In this article, a spectral line emitted by an atom or molecule (throughout the article, spectral lines seen in emission ere described; however, the theory applies equally well to the absorption of radiation in plasmas) has a finite width and there are three distinct physical processes which contribute to this broadening.
Abstract: A spectral line emitted by an atom or molecule (throughout the article, spectral lines seen in emission ere described; however, the theory applies equally well to the absorption of radiation in plasmas) has a finite width and there are three distinct physical processes which contribute to this broadening. The energy levels between which the transition takes place have a natural width, which arises from the reaction of the radiation field on matter. This means that an atom has a finite time in any level before sponteneou decay takes place. Also the emitting atom may be moving in the line of sight, which produces an apparent change in the line frequency through the Doppler effect. Finally, broadening of the spectral line is caused by the interaction of the emitting atom with surrounding particles in the plasma. Thus a detailed analysis of line shapes can yield much information on the density, temperature and motion of plasmas, whether they are high density plasma created in the laboratory, or the l...
TL;DR: In this paper, the effect of velocity-dependent collision broadening on the shape of spectral lines is investigated and it is shown that the modified line shape has a narrower half-width than the conventional Voigt profile.
Abstract: The effect of velocity-dependent collision broadening on the shape of spectral lines is investigated. Computations show that the modified line shape has a narrower half-width than the conventional Voigt profile.
TL;DR: In this paper, a unified treatment of collision broadening due to both intermolecular and wall collisions is given, and it is shown that the combined line shape is nearly Lorentzian even at low pressures, where the mean free path is of the order of magnitude of the dimension of the absorption cell.
Abstract: In order to study the effect of intermolecular collisions on the shape of microwave absorption lines one has to correct the experimental data for the contributions due to the Doppler effect and collisions of molecules with the walls of the absorption cell. The combined effect of the broadening due to the Doppler effect and intermolecular collisions has been treated extensively by Yajima (1961). The effect of wall collisions, however, has only been considered, by Danos and Geschwind (1953), for very low pressures when broadening due to intermolecular collisions can be neglected. A unified treatment is given of collision broadening due to both intermolecular and wall collisions. It is shown that the combined line shape is nearly Lorentzian even at low pressures, where the mean free path is of the order of magnitude of the dimension of the absorption cell.
TL;DR: In this paper, the spectral line width of an irradiation source was investigated for the resonant excitation process and found to be of particular interest when the irradiation spectral width is comparable with atomic (or molecular) line widths.
Abstract: Effects deriving from the finite spectral line width of an irradiation source are investigated for the resonant excitation process and found to be of particular interest when the irradiation spectral width is comparable with atomic (or molecular) line widths. An application of high current interest is laser isotope separation using relatively broad band but tunable dye lasers for selective excitation. Expressions are derived in systematic fashion for the absorption coefficient and for the yield, taking into account three independent line shapes—the first describing the irradiation source, the other two describing Lorentz and Doppler broadening of the atomic (or molecular) medium. Saturation effects are included, but propagation effects are neglected. It is shown that the customary distinction between homogeneous and inhomogeneous atomic-line broadening must be modified if the irradiation is not monochromatic. A further result of practical importance is that there exists an optimum irradiation line width that maximizes the yield for resonant transfer. In this respect, the relatively broad spectral widths characteristic of dye lasers are to be regarded as an advantageous feature, contrary to what is generally assumed.
TL;DR: In this article, an analysis of the line profile from a microwave-excited discharge with allowance for Doppler broadening and fine structure yields the effect of foreign gas pressure on the spectral line shape.
Abstract: Observations are reported of the collision broadening and shift of the hydrogen‐α line by helium, neon, and argon foreign gases. An analysis of the line profile from a microwave‐excited discharge with allowance for Doppler broadening and fine structure yields the effect of foreign gas pressure on the spectral line shape. The classical theory of spectral line impact broadening together with an interatomic potential proposed previously for alkali–noble gas interactions correctly predicts the observed broadening and shift of the line.
TL;DR: In this paper, a rotating radial diffraction grating has been used as beam splitter in order to shift the laser light frequency, which allows a high spatial resolution and allows the removal of the pedestal in the Doppler signal.
Abstract: The optical arrangement for a laser Doppler velocimeter is described. A rotating radial diffraction grating has been used as beam splitter in order to shift the laser light frequency. The advantages are that a high spatial resolution can be obtained and that it allows the removal of the pedestal in the Doppler signal. It also provides a method for determining the position of the measuring volume relative to the wall of the test section. Experimental results are presented.
TL;DR: In this paper, a K-band time domain microwave spectrometer with a plane parallel Fabry-Perot resonator external to the gas cell is described, which yields sensitivities comparable to waveguide spectrometers with various gas cells suitable for collision studies or double resonance experiments.
Abstract: A K‐band time domain microwave spectrometer with a plane parallel Fabry–Perot resonator external to the gas cell is described. A time domain emission technique consisting of a two pulse sequence of a long saturating pulse followed by a short π/2 pulse is used to measure energy relaxation times, which are the Fourier transform of pressure and wall collision broadened linewidth independent of Doppler broadening. The flexible resonator configuration yields sensitivities comparable to waveguide spectrometers with various gas cells suitable for collision studies or ir‐double‐resonance experiments.
TL;DR: In this paper, a procedure for extracting nuclear lifetimes from the Doppler-broadened γ-ray lineshapes in multiple Coulomb excitation was described, where the statistical tensors calculated using rotational matrix elements according to the Winther-de Boer MCE computer program gave a lineshape practically independent of the values of the matrix elements used.
TL;DR: In this paper, the suitability of a tunable laser source oscillating simultaneously in many longitudinal modes for two-photon spectroscopy without Doppler broadening is demonstrated.
TL;DR: In this paper, the Balmer-β spectral line is observed during proton bombardment of a copper single crystal and the lineshape has been studied as a function of impact energy (10 − 40 keV) and angle of incidence of the protons with respect to the surface normal.
TL;DR: In this article, a unified treatment of molecular attenuation and phase dispersion is formulated whereby results of molecular physics are translated into frequency-, temperature-, and pressure-dependencies for O/sub 2/MS spectra.
Abstract: Radio wave propagation in the 40-140-GHz band through the first hundred kilometers of the clear atmosphere is strongly influenced by many (> 30) lines of the oxygen microwave spectrum (O/sub 2/-MS) and to a lesser extent by water vapor. A unified treatment of molecular attenuation and phase dispersion is formulated whereby results of molecular physics are translated into frequency-, temperature-, and pressure-dependencies. The propagation factors are developed for O/sub 2/ continuum---(h 20 km) spectra taking into account pressure-broadening (h 40 km), and Doppler broadening (h >60 km). The influence of water vapor is discussed briefly. The filter characteristics of dry air are evaluated for various path models. Examples of computer plots of attenuation and dispersion rates are given as a function of altitude h for homogeneous, zenith, and tangential path geometries through the 1962 U. S. standard atmosphere.
TL;DR: In this paper, spectral line profiles of the D1 and D2 sodium line emission from the twilight and the nightglow have been obtained by means of a 150 mm aperture Fabry-Perot interferometer.
Abstract: Spectral line profiles of the D1 and D2 sodium line emission from the twilight and the nightglow have been obtained by means of a 150 mm aperture Fabry-Perot interferometer. The observed doppler broadening of the twilight profiles yields a temperature for the emitting atoms of (210 ± 15) K, in good agreement with the expected temperature of the sodium layer at ∼ 90 km. By way of contrast, the nightglow line profiles are found to be much broader, their width yielding an apparent temperature of (600 ± 50) K. It is shown that chemiexcitation is the most likely process which imparts kinetic energies in excess of ambient thermal values to the emitting atoms.
TL;DR: The effect of microturbulence is due to an increase in the width of the Doppler core of the line absorption coefficient with the result that the total intensities (equivalent widths) of the Fraunhofer lines at which saturation effects occur are also enhanced as discussed by the authors.
Abstract: Since 1934, when Struve and Elvey introduced the concept of microturbulence for spectral line broadening in addition to pressure and thermal Doppler broadening, this mechanism has frequently been used in the analysis of stellar spectra. According to the discussions in standard textbooks on stellar spectra the effect of microturbulence is due to an increase in the width of the Doppler core of the line absorption coefficient with the result that the total intensities (equivalent widths) of the Fraunhofer lines at which saturation effects occur are also enhanced. Thus the flat part of the curve of growth is raised.
TL;DR: In this paper, the correlation between Doppler and collisional broadening has been considered in detail for radiation in which the lower level of the transition is broadened by the resonance interaction.
Abstract: The correlation between Doppler and collisional broadening has been considered in detail for radiation in which the lower level of the transition is broadened by the resonance interaction. It is found that rather than a single Voigt profile, the profile of the radiation is essentially a sum of Voigt profiles. Although the widths of these profiles vary by some 40%, the over-all line shape is very close to the single Voigt shape obtained when correlation effects are neglected.
01 Dec 1975
TL;DR: In this article, a Monte Carlo analysis of the Doppler-shift attenuated line shapes measured in a γ-ray spectrometer at angles 0° and 90° to the proton beam is presented.
TL;DR: In this article, a model for predicting the shapes of Doppler-broadened spectral lines due to deexcitation by photon emission of excited neutral atoms backscattered from solids is presented.
TL;DR: In this article, it was shown that Doppler radar measurements of the changes with height of the average fall speeds of solid precipitation particles can be used together with radiosonde data to distinguish between growth of ice particles by riming and growth by deposition from the vapor phase.
Abstract: It is shown that Doppler radar measurements of the changes with height of the average fallspeeds of solid precipitation particles can be used together with radiosonde data to distinguish between growth of ice particles by riming and growth by deposition from the vapor phase. Under some conditions this information can be deduced from real-time observations, but generally spectral broadening by turbulence requires that the velocity measurements be time-averaged. Examples of the use of this technique to deduce information on the modes of growth of ice particles in natural and in artificially seeded clouds are given.