Journal of Physics B Atomic Molecular and Optical Physics

Coherence analysis of the He 1s4f state

Jingbo B. Wang, C M Maloney, D. H. Madison

Published Jan 1, 1999• 2 citations

Abstract

In this paper, we present the first theoretical calculation of the Stokes parameters for the singlet-triplet mixed 1s4f state of helium, which is excited coherently by electron impact. Satisfactory agreement with recent measurements is obtained.

DOI: 10.1088/0953-4075/32/5/002

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Journal of Physics B Atomic Molecular and Optical Physics

Coherence analysis of the He 1s4f state

Jingbo B. Wang, C M Maloney, D. H. Madison

Published Jan 1, 1999• 2 citations

Publisher

Abstract

DOI: 10.1088/0953-4075/32/5/002

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In this paper, we present a detailed theoretical description for the coherent electron-impact excitation, the subsequent time evolution, and the cascading decay process of the singlet-triplet mixed $1s4f$ state of helium. The excitation amplitude and phase of each sublevel of this state are related to measurable coincidence intensities and polarizations of the emitted photons. It is found that the intensity and polarization of the emitted photons are time modulated due to the singlet and triplet mixing in the $1s4f$ state.In this paper, we present a detailed theoretical description for the coherent electron-impact excitation, the subsequent time evolution, and the cascading decay process of the singlet-triplet mixed $1s4f$ state of helium. The excitation amplitude and phase of each sublevel of this state are related to measurable coincidence intensities and polarizations of the emitted photons. It is found that the intensity and polarization of the emitted photons are time modulated due to the singlet and triplet mixing in the $1s4f$ state.

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In this paper, we present a detailed theoretical description for the coherent electron-impact excitation, the subsequent time evolution, and the cascading decay process of the singlet-triplet mixed

1s4f

state of helium. The excitation amplitude and phase of each sublevel of this state are related to measurable coincidence intensities and polarizations of the emitted photons. It is found that the intensity and polarization of the emitted photons are time modulated due to the singlet and triplet mixing in the

1s4f

state.

The Stokes parameters

{P}_{1}

{P}_{2}

{P}_{3}

, and

{P}_{4}

have been measured in a scattered electron-polarized cascade photon correlation study of the

4^{1}F

state of helium excited by 29.6 eV electron impact. This is the first detailed experimental study of electron impact excitation leading to the transfer of three units of angular momentum. The data are expected to be influenced by the breakdown of

\mathrm{LS}

coupling for $L\ensuremath{\ge}3$ states, even in a simple system like helium, providing a further challenge for theory.

N=1

) ionization threshold. The present theory takes full account of the singlet-triplet mixing among the singly excited states with principal quantum numbers $n\ensuremath{\lesssim}10$. The model predicts the enhancement of transition probabilities to triplet final states due to the field-induced mixing. In particular, for a field strength of 9.17 kV/cm, polarization of incident photons perpendicular to the field, and a 4 meV broad excitation function tuned to the

1s6p\phantom{\rule{0.16em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}P

states, the $1s6\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ and $1s5\ensuremath{\ell}\ensuremath{\rightarrow}1s2p\phantom{\rule{0.16em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}P$ emitted photon yields are predicted to be about 70 times and 20 times lower, respectively, than the photon yields for transitions to the corresponding singlet final states.