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Journal of Physics B Atomic and Molecular Physics

Collisional processes in sodium vapour optically excited to the 3P state: asymptotic calculations

Pawel Kowalczyk

Published Mar 14, 1984• 23 citations
Publisher

Abstract

Studies two mechanisms for the non-resonant population of the sodium 4D state when sodium vapour is optically excited to the 3P state. They are the energy-pooling collision of two 3P-excited atoms and the radiative collision involving a laser photon. Both processes are considered in the region of large interatomic distances. Results are compared with experimental data.

DOI
10.1088/0022-3700/17/5/021

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Acta Physica Sinica•Jan 1, 1996•0 citations
Studies two mechanisms for the non-resonant population of the sodium 4D state when sodium vapour is optically excited to the 3P state. They are the energy-pooling collision of two 3P-excited atoms and the radiative collision involving a laser photon. Both processes are considered in the region of large interatomic distances. Results are compared with experimental data.
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 .
Abstract. The cross sections for the Na.4D/! Na.4F / 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 Na.4D / ! Na.4F / 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 3D! 3P and 4D! 3P transitions. The measurements yield the following cross section values for those
The recently observed efficient ionization of sodium vapor by a laser tuned to the sodium resonance line can be explained in terms of the large population of resonance-state atoms created by laser-induced radiative equilibrium. This large population of excited atoms represents (a) a reservoir of energy that can rapidly be transferred to the free electrons via superelastic collisions and (b) a source of pseudo-ground- state atoms possessing a much reduced ionization energy. Three-photon ionization is proposed as the mechanism for creation of the primary pool of free electrons.
We report studies of collision-induced features of the 3S(1/2) yields 3P(1/2) yields 4D(3/2) two-photon absorption in atomic sodium vapor undergoing collisionss with several rare gas perturbers. The results yield the collisional redistribution function which describes the nonresonant excitation of the 3P(1/2) intermediate state. Good agreement with theory is obtained only if effects of 3P(1/2) in equilibrium with 3P(3/2) state-changing collisions are included in the calculations. Results are used to obtain a value for a pressure broadening coefficient in the Na-Kr system. (Author)
The strong radiative single photon coupling between two excited states of sodium atoms (3p and 4d) has been studied at high intensities, exceeding 10 9 W cm -2 . These excited states are probed by Raman-like resonant five-photon ionization processes. Using two tunable lasers the authors have observed that the doubly resonant process does not occur. In the model picture of photon-dressed atomic levels, this situation can be described as an avoided crossing, with a large minimum separation of 30 cm -1 .
The collisional energy pooling process in a sodium vapor [ Na(3PJ)+Na(3PJ′)→Na(nLJ″)+Na(3S1/2)] is experimentally investigated. At sufficiently low sodium densities,such that only the optically excited 3PJ state is significantly populated, the ratios of nLJ″ fluorescence intensities and the relative density of Na(3P1/2) versus the density of Na(3P3/2) are measured. The ratios of rate coefficients k(nLJ′)(J, J′) relative to k5S(3/2,3/2) are given for nLJ″= 4D3/2, 4D5/2, 4F5/2, 4F7/2, and 5S1/2, each for J = J′ =1/2 and 3/2. At high sodium densities, the 3P states are populated in nearly statistical ratios, the ratios of the k(nLJ″)(1/2,3/2) relative to k5S(3/2,3/2) are obtained.