Doppler broadening

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

3 kW, 0.2 nm narrow linewidth linearly polarized all-fiber laser based on a compact MOPA structure

Abstract: In this work, we realize a high-power, narrow linewidth, linearly polarized laser output based on a compact all-fiber polarization maintaining (PM) master oscillator power amplifier. The seed is a fiber oscillator laser (FOL) with few-longitudinal-mode for spectral broadening suppression. The spectral broadening characteristics in the FOL seed and in the PM-amplifier with different pumping schemes are studied experimentally and theoretically. The effect of different types of fibers in the amplifier on spectral broadening is also analysed theoretically. Finally, we demonstrate a narrow linewidth linearly polarized all-fiber amplifier operating at the maximum output power of 3.08 kW with a 3 dB linewidth of 0.2 nm. The polarization extinction ratio is measured to be larger than 93.5% and the M2 maintains lower than 1.45 in the power scaling process. To the best of our knowledge, this is the highest demonstrated output power for narrow linewidth linearly polarized all-fiber lasers with the charactristics of low cost and a compact structure.

Spectroscopic measurements of ion temperature in ATC tokamak with RF and neutral-beam heating

Abstract: Measurements of ion temperatures in the ATC tokamak by means of Doppler broadening of various ion lines are described, and typical results presented for the various auxiliary heating experiments: compression, neutral beam, lower hybrid and ion cyclotron frequency heating. Radial resolution of the temperature measurements is achieved by utilizing spectrum lines of ions of different ionization potentials: O VII λ 1623 A, C V λ 2271 A and C IV λ 1548 A, which are emitted from regions of different electron temperature. Measurement at a given radial location is performed as a function of time by repeated scanning of the line contour in times 1.5–3.0 ms. The results indicate variations of heating efficiency with location and with power input level.

Post-implantation annealing of SiC studied by slow-positron spectroscopies

Abstract: The effects of post-implantation annealing of damage in 6H-SiC caused by ion implantation at two different fluences have been studied by monoenergetic positron Doppler broadening and lifetime techniques. The measurements are supported by new calculations of positron lifetimes in vacancy clusters in SiC. At both fluences two defected layers are identified and characterized by depth and defect type as a function of annealing temperature. The results indicate that it is impossible to remove the radiation damage by annealing at temperatures up to .

Observation of ultra-narrow electromagnetically induced transparency and slow light using purely electronic spins in a hot atomic vapor

Abstract: Electromagnetically induced transparency (EIT) is observed in gaseous 4He at room temperature. Ultra-narrow (less than 10 kHz) EIT windows are obtained for the first time for purely electronic spins in the presence of Doppler broadening. The positive role of collisions is emphasized through measurements of the power dependence of the EIT resonance. The measurement of slow light opens up possible ways to applications.

Solar bursts gyrosynchrotron emission from three-dimensional sources

Abstract: Aims. In this study we have analyzed the spectral and spatial characteristics of gyrosynchrotron emission and the polarization of solar bursts in a highly inhomogeneous medium. Our main goal was to investigate the effects of the geometry of the source on the resulting spectrum. Methods. The SOHO/EIT and TRACE high resolution images revealed structured magnetic configurations in detail over solar active regions. In our method, we represent the magnetic field geometry by three-dimensional structures obtained from magnetic field extrapolation, tomography, or any geometry that resembles the observed structures. The gyrosynchrotron radiation was numerically calculated through a modified version of Ramaty’s code. Results. We calculated the radiation produced by non-thermal electron distributions in this complex environment and solved the radiative transfer equation. The results, presented in brightness distribution maps, polarization maps, and spectra, are discussed. Our numerical results agree with statistical analyses of observed spectra present in the literature. We note a spectral broadening due to the spatial and intensity inhomogeneity of the magnetic field and no center-to-limb variations, which cannot be explained by homogeneous source models. The computed maps revealed a non uniform brightness distribution, with small-scale structures, and different spatial characteristics in each frequency. Also, we found different spectral characteristics at different regions of the emitting source. Polarization maps reveal its high dependence on geometry and on the position of the source on the solar disk.