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Doppler broadening
About: Doppler broadening is a research topic. Over the lifetime, 5509 publications have been published within this topic receiving 92552 citations.
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TL;DR: In this article, the authors focus on the theory of spectral broadening mechanisms involved during Compton scattering of laser photons from relativistic electron beams and propose a design taking these mechanisms into consideration.
Abstract: The design of narrow-band Compton scattering sources for specific applications using nuclear resonance fluorescence (NRF) is presented. NRF lines are extremely narrow ($\ensuremath{\Delta}E/E\ensuremath{\sim}{10}^{\ensuremath{-}6}$) and require spectrally narrow sources to be excited selectively and efficiently. This paper focuses on the theory of spectral broadening mechanisms involved during Compton scattering of laser photons from relativistic electron beams. It is shown that in addition to the electron beam emittance, energy spread, and the laser parameters, nonlinear processes during the laser-electron interaction can have a detrimental effect on the gamma-ray source bandwidth, including a newly identified weakly nonlinear phase shift accumulated over the effective interaction duration. Finally, a design taking these mechanisms into consideration is outlined.
53 citations
TL;DR: In this article, a methodology to allow on-the-fly Doppler broadening of neutron cross sections for use in Monte Carlo codes has been developed based on a combination of Taylor series expansions and asymptotic series expansions.
Abstract: A methodology to allow on-the-fly Doppler broadening of neutron cross sections for use in Monte Carlo codes has been developed. The Monte Carlo code only needs to store 0K cross sections for each isotope and the method will broaden the 0K cross sections for any isotope in the library to any temperature in the range 77K-3200K. The methodology is based on a combination of Taylor series expansions and asymptotic series expansions. The type of series representation was determined by investigating the temperature dependence of U238 resonance cross sections in three regions: near the resonance peaks, mid-resonance, and the resonance wings. The coefficients for these series expansions were determined by a regression over the energy and temperature range of interest. Since the resonance parameters are a function of the neutron energy and target nuclide, the ψ and χ functions in the Adler-Adler multi-level resonance model can be represented by series expansions in temperature only, allowing the least number of terms to approximate the temperature dependent cross sections within a given accuracy. The comparison of the broadened cross sections using this methodology with the NJOY cross sections was excellent over the entire temperature range (77K-3200K) and energy range. A Monte Carlo code was implemented to apply the combined regression model and used to estimate the additional computing cost which was found to be less than <1%.
53 citations
TL;DR: It is shown that extending the model to a large number of states results in LO phonon-induced spectral broadening and complete decoherence of the optical response.
Abstract: It is widely believed that, due to its discrete nature, excitonic states in a quantum dot coupled to dispersionless longitudinal-optical (LO) phonons form everlasting mixed states (exciton polarons) showing no line broadening in the spectrum. This is indeed true if the model is restricted to a limited number of excitonic states in a quantum dot. We show, however, that extending the model to a large number of states results in LO phonon-induced spectral broadening and complete decoherence of the optical response.
53 citations
TL;DR: In this paper, the excitation spectrum of the L 3 -M 5 X-ray emission of Dy compounds in the pre-edge region of Dy L 3 Xray absorption near edge structure (L 3 -XANES) is theoretically investigated based upon the coherent second order optical formula with multiplet coupling effects.
Abstract: The excitation spectrum of the L 3 -M 5 X-ray emission of Dy compounds in the pre-edge region of Dy L 3 X-ray absorption near edge structure (L 3 -XANES) is theoretically investigated based upon the coherent second order optical formula with multiplet coupling effects. The spectral broadening of the excitation spectrum is determined by the M 5 core hole lifetime, being free from the L 3 core hole lifetime. The fine pre-edge structure of the L 3 edge due to the 2 p →4 f quadrupole transition can be seen in the excitation spectrum, while this structure is invisible in the conventional XANES, in agreement with the recent experimental results. We clarify the conditions for the excitation spectrum to be regarded as the absorption spectrum with a smaller width. The resonant X-ray emission spectra for various incident photon energies around the L 3 edge are also calculated.
53 citations
TL;DR: In this paper, a T -matrix expansion is used to derive Baranger's impact approximation, which is shown to be exact in the low density limit, provided that either the mass of the foreign particles is very different from that of the radiating atoms, or the scattering is predominantly in the forward direction.
52 citations