Transfer of radiation in spectral lines

Ivanov, V. V.

doi:10.6028/nbs.sp.385

Cited by 94 publications

(49 citation statements)

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“…Since the experiments were performed at low number densities of sodium atoms (n 3s ∼10 10 cm −3 ), lineshape modifications by radiation trapping can be disregarded [7,8]. We attribute the observed lineshape effects to op-tical pumping, which leads to depletion broadening of spectral lines [9,10].…”

Section: Introductionmentioning

confidence: 96%

Broadening and intensity redistribution in theNa(3p)hyperfine excitation spectra due to optical pumping in the weak excitation limit

et al. 2008

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Detailed analysis of spectral line broadening and variations in relative intensities of hyperfine spectral components due to optical pumping is presented. Hyperfine levels of sodium 3p 1/2 and 3p 3/2 levels are selectively excited in a supersonic beam at various laser intensities under the conditions when optical pumping time is shorter than transit time of atoms through the laser beam. The excitation spectra exhibit significant line broadening at laser intensities well below the saturation intensity, and redistribution of intensities of hyperfine spectral components is observed, which in some cases is contradicting with intuitive expectations. Theoretical analysis of the dynamics of optical pumping shows that spectral line broadening depends sensitively on branching coefficient of the laser-driven transition. Analytical expressions for branching ratio dependent critical Rabi frequency and critical laser intensity are derived, which give the threshold for onset of noticeable line broadening by optical pumping. The critical laser intensity has its smallest value for transitions with branching coefficient equal to 0.5, and it can be much smaller than the saturation intensity. Transitions with larger and smaller branching coefficients are relatively less affected. The theoretical excitation spectra were calculated numerically by solving density matrix equations of motion using the split propagation technique, and they well reproduce the observed effects of line broadening and peak intensity variations. The calculations also show that presence of dark (i.e., not laser-coupled) Zeeeman sublevels in the lower state results in effective branching coefficients which vary with laser intensity and differ from those implied by the sum rules, and this can lead to peculiar changes in peak ratios of hyperfine components of the spectra.

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Section: Introductionmentioning

confidence: 96%

Broadening and intensity redistribution in theNa(3p)hyperfine excitation spectra due to optical pumping in the weak excitation limit

et al. 2008

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“…It is extremely impressive that the standard estimates of the Lyman α escape probability, which were used in the first papers on cosmological recombination, and the Sobolev approximation give such precise (better than 5-10%) answers, even though they are based on two incorrect assumptions as mentioned above. It is well known that the principal difference (from a physical point of view) between the cases of partial and complete redistribution does not influence the final result very much in the majority of astrophysical applications (Ivanov 1973). However, the enormous requirements of accuracy of theoretical estimates in the era of precise cosmology change the situation, and force us to search for percent level corrections to the escape of Ly α photons from resonance during the epoch of cosmological recombination.…”

Section: Introductionmentioning

confidence: 99%

Time-dependent corrections to the Ly αescape probability during cosmological recombination

Chluba

Sunyaev

2009

A&A

118

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We consider the effects connected with the detailed radiative transfer during the epoch of cosmological recombination on the ionization history of our Universe. We focus on the escape of photons from the hydrogen Lyman α resonance at redshifts 600 z 2000, one of two key mechanisms defining the rate of cosmological recombination. We approach this problem within the standard formulation, and corrections due to two-photon interactions are deferred to another paper. As a main result we show here that within a non-stationary approach to the escape problem, the resulting correction in the free electron fraction, N e , is about ∼1.6-1.8% in the redshift range 800 z 1200. Therefore the discussed process results in one of the largest modifications to the ionization history close to the maximum of Thomson-visibility function at z ∼ 1100 considered so far. We prove our results both numerically and analytically, deriving the escape probability, and considering both Lyman α line emission and line absorption in a way different from the Sobolev approximation. In particular, we give a detailed derivation of the Sobolev escape probability during hydrogen recombination, and explain the underlying assumptions. We then discuss the escape of photons for the case of coherent scattering in the lab frame, solving this problem analytically in the quasi-stationary approximation and also in the time-dependent case. We show here that during hydrogen recombination the Sobolev approximation for the escape probability is not valid at the level of ΔP/P ∼ 5-10%. This is because during recombination the ionization degree changes significantly over a characteristic time Δz/z ∼ 10%, so that at percent level accuracy the photon distribution is not evolving along a sequence of quasi-stationary stages. Non-stationary corrections increase the effective escape by ΔP/P ∼ +6.4% at z ∼ 1490, and decrease it by ΔP/P ∼ −7.6% close to the maximum of the Thomson-visibility function. We also demonstrate the crucial role of line emission and absorption in distant wings (hundreds and thousands of Doppler widths from the resonance) for this effect, and argue that the final answer probably can only be given within a more rigorous formulation of the problem using a two-or multi-photon description.

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“…The local uniformity means that the specific intensity at a given point of the surface can be calculated neglecting the nonuniformity of the flux distribution over the surface, that is, the nonuniformity of T s . Almost all models of neutron-star photospheres assume the radiative and local thermodynamic equilibrium (LTE; see [191] for a discussion of this and alternative approximations). Under these conditions, it is sufficient to solve a system of three basic equations: equations of radiative transfer, hydrostatic equilibrium, and energy balance.…”

Section: Radiative Transfermentioning

confidence: 99%

“…In general, the radiative transfer equation includes an integral of I ω not only over angles, but also over frequencies, and contains, with account of polarization, a vector of Stokes parameters instead of I ω , while the scattering cross section is replaced by a matrix. A detailed derivation of the transfer equations for polarized radiation is given, e.g., in [192], and solutions of the radiative transfer equation with frequency redistribution are studied in [191].…”

Section: Radiative Transfermentioning

confidence: 99%

Atmospheres and radiating surfaces of neutron stars

Potekhin¹

2014

Phys.-Usp.

116

129

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The early 21st century witnesses a dramatic rise in the study of thermal radiation of neutron stars. Modern space telescopes have provided a wealth of valuable information which, when properly interpreted, can elucidate the physics of superdense matter in the interior of these stars. This interpretation is necessarily based on the theory of formation of neutron star thermal spectra, which, in turn, is based on plasma physics and on the understanding of radiative processes in stellar photospheres. In this paper, the current status of the theory is reviewed with particular emphasis on neutron stars with strong magnetic fields. In addition to the conventional deep (semi-infinite) atmospheres, radiative condensed surfaces of neutron stars and "thin" (finite) atmospheres are considered.

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Transfer of radiation in spectral lines

Cited by 94 publications

References 0 publications

Broadening and intensity redistribution in theNa(3p)hyperfine excitation spectra due to optical pumping in the weak excitation limit

Broadening and intensity redistribution in theNa(3p)hyperfine excitation spectra due to optical pumping in the weak excitation limit

Time-dependent corrections to the Ly αescape probability during cosmological recombination

Atmospheres and radiating surfaces of neutron stars

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