Doppler broadening

About: Doppler broadening is a research topic. Over the lifetime, 5509 publications have been published within this topic receiving 92552 citations.

Absorption spectra of quantum aggregates interacting via long-range forces.

Abstract: We present a simple formula by which the shape of the absorption spectrum of an aggregate of quantum "monomers" (cold atoms, molecules, quantum dots, nanoparticles, etc.) interacting via dipole-dipole forces can be calculated from the averaged spectrum of the quantum monomer itself. Spectral broadening, due to a wide variety of causes, is included explicitly so that the formula is applicable not only to the idealization of a discrete spectrum but also to the practical situation of a continuously broadened spectrum. In simple cases, analytic results are obtained showing the strong dependence of the aggregate spectrum on the precise nature of the broadening of the quantum monomer spectrum. The formula is compared with results of exact diagonalization of model aggregate Hamiltonians and with experiment.

Inhomogeneous broadening of infrared and Raman spectral bands of amorphous and polycrystalline thin films

Abstract: Infrared and Raman spectroscopy are used to examine effects of solid structure on vibrational line shapes in thin solid films of CO2 and N2O prepared by vapor deposition. A new method is described for forming films consisting of weakly‐interacting microcrystals by deposition of the solute in an argon matrix followed by complete evaporation of the argon. The infrared absorption bands of these films exhibit inhomogeneous spectral broadening in the range between the transverse and longitudinal frequencies of the bulk crystal. The origin of this broadening is shown to be the dependence of vibrational frequencies on size and shape of the microcrystals due to long‐range dipole interactions. In contrast, the spectra of polycrystalline films formed by direct vapor deposition are the same as for single crystals because the long‐range dipole interactions effectively couple vibrational motions across the grain boundaries. An analysis shows that inhomogenously broadened spectra are obtained whenever the separation be...

Spectral broadening in continuous-wave intracavity Raman lasers

Abstract: Spectral broadening of the fundamental field in intracavity Raman lasers is investigated. The mechanism for the spectral broadening is discussed and the effect is compared in two lasers using Raman crystals with different Raman linewidths. The impact of the spectral broadening on the effective Raman gain is analyzed, and the use of etalons to limit the fundamental spectral width is explored. It was found that an improvement in output power could be obtained by using etalons to limit the fundamental spectrum to a single narrow peak.

Treatment of Nuclear Data for Transport problems Containing Detailed Temperature Distributions

Abstract: This work considers the problem of accurately representing the temperature dependence of neutron cross-section data in neutron transport problems when there are many nuclides and when the temperature distributions vary significantly with both space and time. An approach involving interpolation between nuclear data libraries at various reference temperatures is investigated. Reference nuclear data libraries are obtained by Doppler broadening cross sections to the desired temperatures using the NJOY code system. Several interpolation schemes over various temperature intervals are studied. Interpolated values at intermediate temperatures are compared to NJOY Doppler broadened results for the same temperature. Differences relative to the Doppler broadened results are calculated in order to judge the suitability of the interpolation scheme and temperature interval. The total, elastic scattering, capture, and fission (if applicable) reactions for {sup 238}U, {sup 235}U, natural Zr, {sup 16}O, {sup 10}B and {sup 1}H are considered in this study, over a temperature range of 294 K to 811 K ({approx}70 F to {approx}1000 F). The nuclides and temperature range are selected to best represent typical light water reactor calculations. This work covers only the free-atom cross section and does not explore the many nuances of temperature treatment of nuclear data in the thermalmore » energy range for nuclides where molecular binding effects are significant, e.g., water, beryllium, graphite. Additionally, dilute-average cross sections are used in the unresolved resonance range (URR) for this study. Temperature treatment of probabilistic methods used to construct cross sections in the URR are not considered for this work. The study shows that cross sections can be interpolated within an accuracy of 0.1% over a temperature interval of 111 K (200 F) for {sup 1}H, {sup 10}B, and {sup 16}O. Smaller intervals are required for nuclides with more complex resonance behavior. Some values of the interpolated cross sections for natural Zr, {sup 238}U and {sup 235}U, remain greater than the target 0.1% relative difference even with a 28 K (50 F) interval, suggesting a smaller interval is necessary for these nuclides.« less

Doppler Broadening and Magnetic Field Effects on Some Ion Impurity Spectra Emitted in the Boundary Layer of a Tokamak Plasma

Abstract: Examples are presented of Doppler broadening measurements on singlet, doublet and triplet emission spectra from the following impurity ions found in the boundary layer of the TEXTOR tokamak: Cii, Ciii, Civ, Siii, and Siiii. The shapes of these spectral lines are significantly influenced by the confining magnetic field of some 2T, in some cases exhibiting an appreciable Paschen-Back effect which complicates their appearance. It is shown that reliable values for the particular ion temperature can be obtained from the Doppler widths of the various Zeeman components, when the presence of the magnetic field is properly accounted for. Such temperatures derived from partially ionised impurity species should, however, be cautiously interpreted, as the ions in question probably do not exist for long enough in the particular ionisation stage to achieve thermal equilibrium with the background deuterons and protons. This interpretation of our results is supported by a simple one-dimensional model of ionisation and collisional heating processes in the plasma boundary.