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Physical Review A

Cascade Effects in Certain Atomic Lifetime Measurements

Roald K. Wangsness

Published Apr 1, 1971• 12 citations
Publisher

Abstract

A semiclassical discussion is given of a simple case of the Hanle effect when the population of the level of interest varies with time because of decays to it from higher levels excited by collisions. It is found that the width of the intensity-vs-applied-field curve is no longer simply related to the lifetime of this single level, but depends on the relative populations and lifetimes of all other participating levels. It is shown by examples that, unless these effects are taken into account, the lifetimes deduced from the measurements can be greatly in error.

DOI
10.1103/physreva.3.1275

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Mean-life Measurements in He I by the Hanle Effect on High-Velocity Atoms Excited in a Gaseous Target

M. Carré, Jean Desesquelles, Maurice Dufay +1 more

Mean lives of He I are deduced from the Hanle curves for high-velocity atoms excited in a gaseous target. For long---mean-life levels we observed oscillations in agreement with a partial precession of the dipoles around the magnetic field. For the $3p^{1}P$ level, the Hanle curve is not perturbed by self-absorption using this method, and the measured mean life (1.8\ifmmode\pm\else\textpm\fi{}0.1 nsec) is in good agreement with the theoretical value.

Physical Review Letters•Nov 22, 1971•19 citations
A semiclassical discussion is given of a simple case of the Hanle effect when the population of the level of interest varies with time because of decays to it from higher levels excited by collisions. It is found that the width of the intensity-vs-applied-field curve is no longer simply related to the lifetime of this single level, but depends on the relative populations and lifetimes of all other participating levels. It is shown by examples that, unless these effects are taken into account, the lifetimes deduced from the measurements can be greatly in error.
Alignment cascade phenomena have been studied in the neon 2p levels (Paschen notation) Hanle effect and double resonance techniques in a mild discharge. The levels are aligned directly by an optical excitation mechanism. Most 2p levels show evidence of alignment cascade from the 2s 4 , 3s 1 or 3d levels below 0.1 Torr; addition of argon impurities greatly enhances the cascade signal relative to the direct alignment signal. Data used previously in pressure broadening studies are shown to be free of cascade errors and are used to establish upper limits for the 2p level life times. A correction for coherence narrowing is estimated; this gives natural life times systematically less than those obtained by methods in which cascade effects are not carefully eliminated. In common with other Hanle effect measurements for these levels the values are marginally smaller than the threshold life times of Bennett and Kindlmann (1966).
The lifetimes of the gallium 52S125^{2}S_{\frac{1}{2}}52S21​​ state, the indium 62S126^{2}S_{\frac{1}{2}}62S21​​ state, and the thallium 72S127^{2}S_{\frac{1}{2}}72S21​​ state were measured using the zero-field level-crossing (Hanle-effect) technique. The life-times obtained were (6.8\ifmmode\pm\else\textpm\fi{}0.3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$, (7.0\ifmmode\pm\else\textpm\fi{}0.3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$, and (7.45\ifmmode\pm\else\textpm\fi{}0.2) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$ sec, respectively. Anomalous contributions to the level-crossing signals, from the wavelength dependence of the exciting light intensity and self-absorption by the fluorescing atomic beam, were investigated in detail.
Mean lives of He I are deduced from the Hanle curves for high-velocity atoms excited in a gaseous target. For long---mean-life levels we observed oscillations in agreement with a partial precession of the dipoles around the magnetic field. For the 3p1P3p^{1}P3p1P level, the Hanle curve is not perturbed by self-absorption using this method, and the measured mean life (1.8\ifmmode\pm\else\textpm\fi{}0.1 nsec) is in good agreement with the theoretical value.