Doppler broadening

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

The effects of numerical resolution on hydrodynamical surface convection simulations and spectral line formation

Abstract: The computationally demanding nature of radiative-hydrodynamical simulations of stellar surface convection warrants an investigation of the sensitivity of the convective structure and spectral synthesis to the numerical resolution and dimension of the simulations, which is presented here. With too coarse a resolution the predicted spectral lines tend to be too narrow, reflecting insufficient Doppler broadening from the convective motions, while at the currently highest affordable resolution the line shapes have converged essentially perfectly to the observed profiles. Similar conclusions are drawn from the line asymmetries and shifts. In terms of abundances, weak FeI and FeII lines show a very small dependence (~0.02 dex) while for intermediate strong lines with significant non-thermal broadening the sensitivity increases (~0.10 dex). Problems arise when using 2D convection simulations to describe an inherent 3D phenomenon, which translates to inaccurate atmospheric velocity fields and temperature and pressure structures. In 2D the theoretical line profiles tend to be too shallow and broad compared with the 3D calculations and observations, in particular for intermediate strong lines. In terms of abundances, the 2D results are systematically about 0.1 dex lower than for the 3D case for FeI lines. Furthermore, the predicted line asymmetries and shifts are much inferior in 2D. Given these shortcomings and computing time considerations it is better to use 3D simulations of even modest resolution than high-resolution 2D simulations.

Speed-dependent line profile: A test of a unified model from the Doppler to the collisional regime for molecule-molecule collisions

Abstract: A speed-dependent line profile combining soft and hard fully correlated Dicke-narrowing collisions was recently successfully tested on Ar-broadened H2 spectra in a wide density and temperature range. A further test for mixtures of H2 in nitrogen molecules (instead of Ar atoms) is presented. This test is also based on high resolution Raman investigation of the isotropic Q(1) line of H2 from low to high density at various temperatures. The same consistency of the speed-dependent line profile as for H2–Ar is obtained for H2–N2 through a remarkable agreement with all the data by using a unique set of four parameters (the collisional width and shift, the kinetic frequency, and a characteristic velocity memory parameter). The present study is a preliminary step for the hydrogen CARS thermometry in H2–air flames at high pressure.

Optical absorption and ionization of silicate glasses

Abstract: Intrinsic, extrinsic (transition metals and hydroxyl), and induced (color centers) absorption of multicomponent silicate glasses in UV, visible and near IR spectral regions are described. Parasitic effects influencing absorption measurements are discussed. Excitation to the intrinsic absorption band results in intrinsic luminescence and ionization followed by color center generation and phosphorescence. The thresholds of electron and hole mobility in glass network are found in the far UV region. The hole-centers generation as a criterion of substance ionization is proposed. A number of nonlinear mechanisms of glass ionization are discussed. Two-photon ionization was detected in alkaline-silicate glasses exposed to high-power laser radiation in nano- and picosecond regimes. Three- photon ionization was detected in lead-silicate glasses. No reliable data on multiphoton ionization (with number of photons more than 3) of glasses are found. Two- and three- photon cooperative self-multiplication of color centers was found in CuCl-doped glasses. Glass matrix ionization by spectral broadening of femtosecond IR pulses is described. Thermal and surface ionization of glass under intense irradiation by pulsed lasers is described.

Analysis of the Relation Between Doppler Spectral Width and Thunderstorm Turbulence

Abstract: A technique to separate ordered flow in a tornadic thunderstorm from the random velocities associated with turbulence is described. The relative importance of the ordered flow shear and turbulence in the broadening of the Doppler velocity spectrum is evaluated by least-squares fitting an assumed linear model of radial velocities to measured ones over an angular analysis domain (about 3° in azimuth and 3° in elevation). Fields and cumulative probabilities of Doppler spectral widths associated with turbulence and velocity shear, of root-mean-square (rms) velocity residuals, and of the turbulent kinetic energy dissipation rates ϵ are presented. In order to estimate ϵ from measurements of Doppler spectral width, the outer scale of the inertial subrange of turbulence must be at least three times larger than the size of the radar's resolution volume. Wind fields synthesized from the Doppler data of two radars are related to the turbulent kinetic energy dissipation rate and rms velocity residual fields....

Enhancement and broadening of extreme-ultraviolet supercontinuum in a relative phase controlled two-color laser field.

Abstract: We experimentally demonstrate the generation of an extreme-ultraviolet (XUV) supercontinuum in argon with a two-color laser field consisting of an intense 7 fs pulse at 800 nm and a relatively weak 37 fs pulse at 400 nm. By controlling the relative time delay between the two laser pulses, we observe enhanced high-order harmonic generation as well as spectral broadening of the supercontinuum. A method to produce isolated attosecond pulses with variable width and intensity is proposed.