Doppler broadening

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

Electromagnetically induced transparency in an inhomogeneously broadened Λ transition with multiple excited levels

Abstract: Electromagnetically induced transparency (EIT) has mainly been modeled for three-level systems. In particular, considerable interest has been dedicated to the $\ensuremath{\Lambda}$ configuration, with two ground states and one excited state. However, in the alkali-metal atoms, which are commonly used, the hyperfine interaction in the excited state introduces several levels which simultaneously participate in the scattering process. When the Doppler broadening is comparable with the hyperfine splitting in the upper state, the three-level $\ensuremath{\Lambda}$ model does not reproduce the experimental results. Here we theoretically investigate the EIT in a hot vapor of alkali-metal atoms and demonstrate that it can be strongly reduced by the presence of multiple excited levels. Given this model, we also show that well-designed optical pumping enables us to significantly recover the transparency.

Propagation and absorption of electromagnetic waves in fully relativistic plasmas

Abstract: The propagation and absorption of electromagnetic waves in a relativistic Maxwellian plasma are investigated by solving the uniform plasma dispersion relation. Both the Hermitian and the anti‐Hermitian parts of the plasma conductivity tensor σ are calculated relativistically. The Bessel functions occurring in σ are not expanded, and many cyclotron harmonic terms are included at high temperatures. The dispersion relation is solved numerically for perpendicular propagation, k∥ =0, where the relativistic effects are maximum and are not masked by Doppler broadening, which has been more thoroughly investigated. It is found that relativistic broadening has a substantial effect on wave dispersion, shifting the extraordinary mode right‐hand cutoff and the upper‐hybrid resonance to higher magnetic field with increasing temperature. Above a critical temperature, the cutoff disappears entirely. There is a broad range of temperatures, 20 keV≤Te ≤500 keV, for which the wavenumber k⊥ differs significantly from both the cold‐plasma value and the vacuum value. This has important implications for ray tracing in relativistic plasmas. Wave damping rates are calculated and compared to results from a previous formulation using the Poynting theorem, in which only the Hermitian part of σ is calculated relativistically.

Study of interface structure of α-Fe/Nd2Fe14B nanocomposite magnets

Abstract: In this study, the interface structure of α-Fe/Nd2Fe14B nanocomposite magnets has been investigated by employing both the positron lifetime spectroscopy and the two-detector Doppler broadening measurements of the positron–electron annihilation γ quanta. Positron lifetime studies show that there are two kinds of interface structures in the magnets. One characterized by a positron lifetime of 155 ps is determined to be the interfacial amorphous layer. The other has a slack atomic structure in which structural free volumes, which were detected to be predominantly surrounded by nonmagnetic atoms Nd and B by the Doppler broadening measurements, have a larger size than that of one to two lattice vacancies of Fe. This is believed to weaken the magnetic exchange coupling between α-Fe and Nd2Fe14B grains in the nanocomposites.