Multiplet-mixing collisions and nearly resonant light scattering

doi:10.1016/0378-4363(78)90102-X

Physica B+C

Volume 95, Issue 2, August–September 1978, Pages 266-276

https://doi.org/10.1016/0378-4363(78)90102-X Get rights and content

Abstract

We study the effect of multiplet-mixing collisions on the strength and the polarization of fluorescence radiation emitted by an atomic multiplet at irradiation with non-saturating resonant or nearly resonant light. Explicit expressions are derived for the strengths and the polarizations in terms of generalized multipole-relaxation matrices, which in turn are expressed in terms of the exact quantum-mechanical collisional cross sections. Multiplet-mixing collisions redistribute the fluorescence over the various emission lines, thereby changing the anisotropy and the polarization of the fluorescence. Special attention is paid to the case of the principal series of alkali atoms.

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Cited by (16)

Laser atomic spectroscopy in flames, gases and beams
1988, Journal of Quantitative Spectroscopy and Radiative Transfer
Some (partly unpublished) laser-induced fluorescence experiments made at our laboratory on the Na-D doublet in flames, gas-filled vapour cells, and an atomic beam in vacuo are reviewed. These experiments relate to the following: the distortion of the fluorescence-emission spectrum of both doublet components by Mollow splitting at strong, near-resonant excitation of one component in an Ar-filled vapour cell; the distortion of the fluorescence-emission spectrum of the laser-excited doublet component by (near-)resonant Rayleigh scattering in a N₂-diluted H₂-O₂ flame; the distortion of the fluorescence-excitation spectrum of the laser-excited doublet component by partial atom trapping in a hyperfine level of the ground-state in an Ar- or N₂-filled vapour cell; and finally the distortion of the saturation curve by similar atom trapping in an atomic beam and the influence of laser-polarization on this curve. Attention is given to the dependence of these effects on the ambient-gas conditions. Also the links between these effects and their possible relevancy for laser-based diagnostic techniques are indicated. The saturation curve of the Mollow triplet is discussed theoretically. A consistent definition of the terms fluorescence and scattering is proposed.
Spectrum and polarization of collision-induced fluorescence and rayleigh components of NaD lines at quasiresonant excitation
1987, Journal of Quantitative Spectroscopy and Radiative Transfer
A theory for radiation redistribution was tested by observing the fluorescence-emission spectrum obtained when sodium atoms, in collision with perturber gas atoms and molecules, were excited within the absorption line-width. A narrow band tunable CW dye laser was used as an irradiating source.
Intensities and polarizations of the collision-induced fluorescence and the Rayleigh component were found to be in good agreement with the values expected from theory.
Collisional depolarization of the Na-D<inf>2</inf> flourescence at line wing excitation in a N<inf>2</inf>-diluted H<inf>2</inf>/O<inf>2</inf> flame at 1 atm
1983, Journal of Quantitative Spectroscopy and Radiative Transfer
The linear polarization of collision induced Na-D₂ line flourescence was measured as a function of detuning of the exciting laser frequency in a N₂-diluted H₂/O₂ flame at 1 atm and 1420K. The fluorescence was observed in a direction perpendicular to the linear polarization vector of the laser beam. The c.w. dye laser was tuned through the red and blue wing of the D₂ line up to 50 Å distance from the line centre. For comparison with theory, additional measurements were made of the polarization of the Rayleigh scattering and of the ratio of its intensity to that of the collision induced fluorescence, as functions of detuning.
Also the rate of disalignment by elastic collisions, D_p, was determined by measuring at resonant excitation, the degree of linear polarization of the D₂ line. The collisional doublet-mixing rates were determined by measuring intensity ratios of the doublet components, while taking into account the polarization of the D₂ line. From these “zero detuning” measurement, the rate for $J = (32)$ « $J = (12)$ transitions was found to be M₁₂ = (5.2±0.3)×10⁹s⁻¹, whereas the rate of disalignment by elastic collisions is D_p = (11±1)×10⁹s⁻¹. From our line-wing measurements we extracted a value of D_p = (11.6±0.3)×10⁹s⁻¹.
Using previously obtained spectral line-profile and fluorescence-quenching measurements, we tested the validity of a theoretical model for collisional depolarization that is based on the usual factorization approximation for the density matrix of radiator plus perturber gas. The predictions of this model were found to agree with our experiments up to detunings of 2Å ( = 540GHz) in the blue D₂-wing, but in the red D₂-wing they did not agree at any detuning. We also tested the validity of a recently developed adiabatic-reorientation model for “strong” collisions. This model, which avoids the factorization approximation, should be applicable in the quasi-static regime at large detunings and predicts that, in our case, the linear polarization tends asymptotically to zero with increasing detuning in the far wings. This prediction is in accordance with our experiments beyond 20 Å ( = 5400GHz) in both wings.
An experimental study of the collisional broadening of the Na-D lines by Ar and N<inf>2</inf> perturbers in flames and vapor cells-II. The line wings
1981, Journal of Quantitative Spectroscopy and Radiative Transfer
In this paper, we report on measurements of the fluorescence-excitation profile of the red Na-D₁ line wing from about 1 cm⁻¹ to 1100 cm⁻¹ and of the blue Na-D₂ line-wing from about 1 cm⁻¹ to 600 cm⁻¹, with respect to the corresponding line centre. We have also measured the fluorescence-excitation profile of the red Na-D₂ and blue Na-D₁ inner (overlapping) line wings from 1 cm⁻¹ with respect to the centre of each of the lines. All these wings were measured in several premixed, laminar, shielded H₂O₂Ar and H₂O₂N₂ flames at 1 atm (1400 K ⪅ T ⪅ 2300 K). We also measured these wings in a vapor cell containing Ar or N₂ perturbers (T ∼ 480 K, p ∼ 0.4 atm) in order to determine the influence of temperature on these wings. Using a tunable CW dye laser as excitation source, we determined the fluorescence-excitation profiles by measuring the total fluorescence intensity while tuning the laser wavelength. In order to specify the contributions that the different kinds of major flame perturbers (Ar, N₂, H₂O) make to the wings, we compared the wing profiles measured in various flames of different flame-gas compositions. In this comparison, the wing profiles were normalized with respect to the line-centre. We compared our measurements of far red Na-D₁ and blue Na-D₂ line-wings ( $Δσ ⪆ 30 cm^{−1}$ ) specified to Ar perturbers (at T = 500 K and T = 2000 K) with the results derived from quasi-static theory using available interaction potential data. In the case of Ar perturbers at T = 500 K, we observed a satellite at about 8 cm⁻¹ from the line-centre on the red Na-D₁ wing: this satellite was absent at T = 2000 K. The position of this red satellite was explained with the help of a set of “modified” potentials, which were constructed for interpreting the collisional Na-D broadening- and shift-rates deduced from our line-core observations and which were reported in Part I of this paper.
Time and frequency dependence of nearly resonant light scattered from collisionally perturbed atoms
1979, Physica B+C
We generalize previous theories of collisional redistribution of near-resonance radiation to the case of a time-dependent incident intensity. In the absence of saturation the relation between the incident and the scattered spectrum is given by a time-dependent redistribution function. In the special case of an incident pulse with an exponential rise and decay we evaluate the time-dependent strength of the Rayleigh or Raman scattering and of the fluorescence. We pay special attention to the restriction on the time resolution resulting from the spectral resolution that is necessary to observe separately the two peaks in the scattered spectrum.
Interference effects in a two-color laser beam interaction with alkali-metal atoms
2000, Physical Review A - Atomic, Molecular, and Optical Physics

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Multiplet-mixing collisions and nearly resonant light scattering

Abstract

Physica

Physica

Opt. Commun.

J. de Phys.

Sov. Phys.-JETP