Doppler broadening

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

Particle-velocity distribution and expansion of a surface-flashover plasma in the presence of magnetic fields.

Abstract: Observations of line-emission Doppler broadening and Doppler shift are used to determine the velocity distributions, parallel and perpendicular to the anode surface, of neutral particles and multiply charged ions in a surface-flashover-produced plasma in a magnetically insulated ion diode. The velocity distributions were found to be nearly Maxwellian with thermal energies of \ensuremath{\simeq}8 eV for neutral particles, \ensuremath{\simeq}20 eV for singly charged ions, and 20--80 eV for doubly and triply charged ions. The plasma-pressure gradient in the magnetic field, obtained from the observed ion temperature and density, and a suggested anomalous plasma conductivity that is approximately ten times lower than the classical conductivity are shown to explain the fast plasma expansion with respect to the magnetic field. Elastic collisions of the 7-eV electrons with the hotter ions cause electron heating. The observed ion velocities in the plasma parallel to the anode account for \ensuremath{\simeq}(1/3 of the velocities in the same directions observed in the diode acceleration gap in a previous experiment.

Disentangling vibronic and solvent broadening effects in the absorption spectra of coumarin derivatives for dye sensitized solar cells.

Abstract: We simulate from first-principles the absorption spectra of five structure-related coumarin derivatives utilized in dye sensitized solar cells (DSSCs), investigating the vibronic and solvent contributions to the position and width of the spectra in ethanol. Ground and excited state potential energy surfaces (PESs) are modeled by Density Functional Theory (DFT) and its time-dependent (TD) expression for the excited state (TD-DFT). The solute vibronic structure associated with the spectrum is calculated by a TD formalism, accounting for both Duschinsky and temperature effects, while solvent inhomogeneous broadening is evaluated according to Marcus' theory, computing the solvent reorganization energy by the state-specific implementation of the polarizable continuum model (PCM) within TD-DFT. We adopted both the standard hybrid PBE0 and the range separated CAM-B3LYP functionals showing that the latter performs better both concerning the vibronic and solvent-induced contributions to the absorption lineshape. The different predictions of the two functionals are then rationalized in terms of the charge transfer (CT) character of the transitions showing that, in this class of compounds, it is strongly dependent on the nuclear structure. Such a dependence introduces a bias in the PBE0 PES that has a drastic impact on the vibronic spectra. We show that both the intrinsic vibronic structure and the solvent broadening play a relevant role in differentiating the absorption width of the five dyes. In this sense, our results provide a guide to understand the sources of spectral broadening of this family of dyes, a valuable help for a rational design of new molecules to improve DSSC devices.

Physical interpretation of bistable unidirectional ring-laser operation

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.

Spectral broadening in femtosecond laser written waveguides in chalcogenide glass

Abstract: Nonlinear spectral broadening to 200 nm, from an initial width of 50 nm, has been demonstrated in gallium lanthanum sulphide glass waveguides from 1540 nm, 200 fs pulses at 30 nJ/pulse. A formation mechanism is presented for these femtosecond laser written waveguides, based on optical characterization and comparisons to previous work. Two different types of waveguide are identified. One has a characteristic long narrow structure and is formed through filamentation caused by self-focusing. The other has a characteristic “teardrop” structure, which is formed by a type IIA photosensitivity mechanism and cumulative heating of glass around a central laser-exposed region.

Rainfall Doppler Velocity Measurements from Spaceborne Radar: Overcoming Nonuniform Beam-Filling Effects

Abstract: For vertical Doppler velocity measurements of a homogeneous rain field, the standard spectral moment estimation techniques commonly used by ground-based and airborne Doppler rain radars can be readily extended for spaceborne application, provided that the radar antenna size is chosen to adequately reduce the satellite motion-induced Doppler spectral broadening. When encountering an inhomogeneous rain field, on the other hand, the nonuniform beam filling (NUBF) causes additional biases on Doppler velocity estimates, which (i) often reach several meters per second, (ii) cannot be corrected with standard spectral moment techniques, and (iii) are strongly dependent on the along-track reflectivity profile within the radar footprint. One approach to overcome this difficulty is to further increase the antenna size such that the radar's horizontal resolution would be sufficiently small to resolve the inhomogeneity in rain cells. Unfortunately, this approach is very challenging in terms of antenna technol...