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Journal of Physics B Atomic and Molecular Physics

Direct observation of a two-photon radiative ionisation collision in crossed Na-Ba atomic beams

Penelope Polak-Dingels, R. E. Bonanno, J Keller, J. Weiner

Published Jan 28, 1982• 7 citations
Publisher

Abstract

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.

DOI
10.1088/0022-3700/15/2/002

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Journal of Physics B Atomic and Molecular Physics•May 28, 1983•8 citations
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.
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We measured the angular distribution of the excited Na atoms from the process Na(Ss)+Kr+h nu to Na(3p)+Kr. The photon energy is detuned by 50 cm -1 from the Na resonance energy and the optical transition can occur only when the atoms are close to each other. The angular resolution allows the observation only of the general structure of the cross section, but not of finer details. We describe the experimental method and the experimental difficulties, especially the origin of a number of competing signals. We discuss the process as a new way of observing the collision Na+Kr, using the photon as a probe.
The cross sections for the excitation energy transfer induced by collisions with He, Ar and Na ground-state atoms have been measured. The sodium atoms in the 4D state have been produced by two-photon excitation using cw laser radiation at 578.89 nm. Within a model which takes into account collisional population and depopulation of the 4F level as well as radiative relaxation (direct or cascade) of the 3D, 4P, 4D and 4F states ending in the 3P level, the rate for the collisional transfer turns out to be related to the ratio of the steady-state populations created in 3D and 4D states. They have been determined by measuring the fluorescence intensities of the and transitions. The measurements yield the following cross section values for those processes investigated: , and , at .
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The authors report direct measurements of the photodissociation of Na 2 + ions created when a Na vapour in the density range 10 12 -10 13 cm -3 is irradiated by a pulsed laser with intensities in the 10 5 -10 6 W cm -2 range. The Na 2 + ions, accelerated by a weak electric field, are photodissociated in a second laser beam tuned to 6040 AA. In a preliminary experiment the Na 2 + ions are formed in the lowest vibrational levels and the measured photodissociation cross section is compared with existing calculations. When the Na vapour is irradiated at one of the 3S 1/2 -3P 1/2,3/2 resonances the photodissociation measurements show the existence of a distribution of rovibrational excited levels of the Na 2 + ions. A discussion is given in terms of associative ionisation in collisions of two Na(3p) atoms. The origin of the Na + ions produced simultaneously with the Na 2 + ions, in the vapour irradiated at resonance, is also discussed.