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Journal of Physics B Atomic and Molecular Physics

Interpretation of the experimental cross section profile of a laser-induced charge exchange process

Anne Débarre, Ph. Cahuzac

Published Dec 14, 1986• 9 citations
Publisher

Abstract

The authors report on the observation of a laser-induced charge exchange process in a Sr + -Ba mixture. Two maxima occur in the cross section profile when the barium atoms are ionised to the final 5p 2 P 1/2 level. The photon energy for each maximum differs from the energy defect of the reaction partners at infinite separation. In the framework of the quasimolecular model, a complete analysis of the profile is derived. The first peak corresponds to the expected assisted signal while the second one is interpreted as a satellite line.

DOI
10.1088/0022-3700/19/23/015

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The authors report on the observation of a laser-induced charge exchange process in a Sr + -Ba mixture. Two maxima occur in the cross section profile when the barium atoms are ionised to the final 5p 2 P 1/2 level. The photon energy for each maximum differs from the energy defect of the reaction partners at infinite separation. In the framework of the quasimolecular model, a complete analysis of the profile is derived. The first peak corresponds to the expected assisted signal while the second one is interpreted as a satellite line.
Laser-induced collisional ionisation of caesium is observed in a strontium-caesium vapour mixture. In their initial state both atomic species are in the ground level. The ionisation of caesium is achieved when the system is illuminated by an intense laser light, the frequency of which is tuned across the resonance line of strontium. The process involves photoabsorption during the collisional interaction. It is monitored by the observation of optical fluorescence after Cs + , e - recombination. The laser-induced collisional ionisation profile, i.e. the variation of the ionisation yield against the laser wavelength is recorded under various experimental conditions.
Experimental studies of two laser-induced charge-transfer reactions in Ca and Sr are presented. In both reactions, a Ca ion collides with an Sr neutral in the presence of a laser field to produce a Ca neutral and an excited Sr ion. The two reactions differ in the final level of the Sr+{\mathrm{Sr}}^{+}Sr+ species. The collision cross sections associated with these reactions are studied as functions of applied laser frequency and power density. The largest cross section induced is equal to ${10}^{\ensuremath{-}16}$ cm2{\mathrm{cm}}^{2}cm2, obtained at a power density of 2\ifmmode\times\else\texttimes\fi{}109{10}^{9}109 W/cm2{\mathrm{cm}}^{2}cm2. Differences in experimental results associated with the two reactions are explained qualitatively by an examination of the potential curves of the CaSr+{\mathrm{Sr}}^{+}Sr+ quasimolecule.
Investigates theoretically a new aspect of radiative collisions on two-photon ionisation of colliding atoms of different species A and B. The authors derive the main characteristics of the resonance appearing in the two-photon ionisation cross section of atom B when the laser frequency is tuned on a resonance transition of atom A which cannot itself be ionised by two-photon absorption. Under some realistic conditions and for reasonable values of the light energy density flux F ( approximately 1 MW cm -2 ), the cross section of the process considered varies as F 2/5 while its width varies as F 1/2 . These predictions are in reasonable agreement with a recent observation on the mixture Sr(A)-Cs(B) by Brechignac et al. (1980).
The laser-induced collisional energy transfer process: Rb(5 2 P 3 2/)+Na(3 2 S 1 2/)+hv implies Rb(5 2 S 1 2/)+Na(3 2 D 3 2.5/2/), is experimentally investigated. The relative transfer cross section or transfer profile is measured versus the frequency of the photon. The far wing of the transfer profile is well interpreted using the quasi-static approximation. However, it is shown that the central part of the profile is reproduced only by taking into account non-adiabatic mixing between molecular levels during the collision.
The authors report the observation of a two-step process in which Na*(4d) is first populated by a radiative collision between Na(3s) and Ba*(6p) in the presence of an intense optical field i.e. Na(3s)+Ba*(6s6p 1 P)+h(cross) omega to Na*(4d)+Ba(6s 2 1 S) followed by photoionisation of the excited sodium Na*(4d)+h(cross) omega to Na + +e. The peak ion intensity is observed at a laser frequency close to the energy difference between Na*(4d) and Ba*(6s6p 1 P), and the magnitude of the cross section for the first step agrees well with theory.