Doppler broadening

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

Spectral broadening of lower-hybrid waves by time-dependent density fluctuations

Abstract: Lower‐hybrid waves injected into tokamaks are scattered by turbulent time‐dependent drift‐wave density fluctuations. This scattering process gives rise to frequency shifts as well as angular deviations. In tokamaks, most of the frequency spreading occurs in a regime where the angular scattering results from multiple scattering events, each event having a small mean‐square scattering angle. A radiative transport equation governing diffusion in both angle and frequency is derived. The solution is obtained in slab geometry via separation of variables and leads to a Mathieu equation. In the limit where the slab thickness l exceeds the typical distance for diffusion through a large angle l s , an explicit generalization of the diffusion solution to the radiative transfer equation is formed. This solution gives the combined angular and frequency spectrum in the scattering layer. In the thick slab limit, the rms frequency width of lower‐hybrid waves emerging from the layer is given by Δω=(ω d / ξ0ρ i ) N ∥ [(M i /m e )β i ]1 / 2 (l/l s ), where ω d and ξ−1 0 are the characteristic angular frequency and correlation length of the drift‐wave turbulence.

Effects of radiator motion on plasma-broadened hydrogen lyman-β

Abstract: For the hydrogen line L-β, broadening in an Ar + -plasma ( N e = 7.2 × 10 16 cm −3 , T = 12,200 K ) has been investigated with the help of a computer simulation of ion broadening taking full account of radiator motion. The anisotropy in Stark broadening for a moving radiator is found to be negligible under these conditions, but Stark profiles depend markedly on the radiator speed. The final line profile (including Stark and Doppler broadening) is nearly the same as the profile obtained by convolution of the Doppler profile with the Stark profile for radiators at rest and fictitious ions with the reduced mass of the atom-ion pair.

Toward a Broadband Astro-comb: Effects of Nonlinear Spectral Broadening in Optical Fibers

Abstract: We propose and analyze a new approach to generate a broadband astro-comb by spectral broadening of a narrowband astro-comb inside a highly nonlinear optical fiber. Numerical modeling shows that cascaded four-wave-mixing dramatically degrades the input comb's side-mode suppression and causes side-mode amplitude asymmetry. These two detrimental effects can systematically shift the center-of-gravity of astro-comb spectral lines as measured by an astrophysical spectrograph with resolution \approx100,000; and thus lead to wavelength calibration inaccuracy and instability. Our simulations indicate that this performance penalty, as a result of nonlinear spectral broadening, can be compensated by using a filtering cavity configured for double-pass. As an explicit example, we present a design based on an Yb-fiber source comb (with 1 GHz repetition rate) that is filtered by double-passing through a low finesse cavity (finesse = 208), and subsequent spectrally broadened in a 2-cm, SF6-glass photonic crystal fiber. Spanning more than 300 nm with 16 GHz line spacing, the resulting astro-comb is predicted to provide 1 cm/s (~10 kHz) radial velocity calibration accuracy for an astrophysical spectrograph. Such extreme performance will be necessary for the search for and characterization of Earth-like extra-solar planets, and in direct measurements of the change of the rate of cosmological expansion.

Inhibition and enhancement of positronium formation in aqueous solutions from the Doppler broadening of annihilation peaks

Abstract: The Doppler broadened positron annihilation line shapes have been determined in aqueous solutions of various inhibiting and enhancing agents of positronium (Ps) formation : H+aq, NO−3, S2−, SCN− and the halide ions. The results confirm that the inhibition is made through electron scavenging by H+aq and NO−3, and through positron capture, to form a bound state, by the other ions. The characteristics and yields of the various positron‐containing species in the solutions are inferred from the deconvoluted experimental line shapes. On referring to the lifetime spectroscopy experimental data, it is found that the yields of positron bound states are lower than expected, and the formation of excited states is hypothesized to account for the discrepancy.