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Journal of Physics B Atomic Molecular and Optical Physics

Coherent beam–foil excitation of 2s1/2and 2p1/2states of hydrogen and antihydrogen atoms in an external electric field

Leonti N Labzowsky, V. Sharipov, Dmitry A. Solovyev, G. Plunien

Published Nov 23, 2006• 0 citations
Publisher

Abstract

A beam–foil experiment is proposed for observation of a phase shift π in a beat intensity of light emitted by hydrogen and antihydrogen atoms in an external electric field. This effect is based on the existence of the terms linear in the electric field in the expression for the radiation probability of an atom. The linear terms have an opposite sign for hydrogen and antihydrogen atoms and lead to such a difference in a beat signal. Experimental conditions for observation of this effect are discussed.

DOI
10.1088/0953-4075/39/24/006

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A beam–foil experiment is proposed for observation of a phase shift π in a beat intensity of light emitted by hydrogen and antihydrogen atoms in an external electric field. This effect is based on the existence of the terms linear in the electric field in the expression for the radiation probability of an atom. The linear terms have an opposite sign for hydrogen and antihydrogen atoms and lead to such a difference in a beat signal. Experimental conditions for observation of this effect are discussed.
An expression is given for the Stark-induced beat signal in the Lyman-$\ensuremath{\alpha}$ radiation from hydrogen atoms in a beam-foil experiment. This expression includes possible contributions to the beat signal from coherent excitation of SSS and PPP states in the beam-foil process. For the case where the electric field is applied parallel to the beam, the coherentexcitation contributions can be separated experimentally from those resulting purely from coherence produced by the electric field, by simply reversing the direction of the electric field.
Four experiments involving individual and combined effects of electric fields and multiple exciter foils on beam-foil-excited hydrogen atoms are described.The use of multiple exciter foils shows that excitation equilibrium does not occur in the thin carbon foils used here. The change of the rate of decay of Ly-α flux emitted by beam-foil excited hydrogen atoms in an electric field has been used to determine the relative populations of the 2s and 2p levels at the foil. The 2s level is overpopulated with respect to the 2p level when one foil is used and two exciter foils enhance the overpopulations. Photoelectric measurements of Ly-α flux and photographic measurements of the decay of Balmer-δ flux emitted by atoms in an electric field show that quasiperiodic intensity variations exist on the decay curve. The variations are attributed to the effect of the electric field but discrepancies arise between the experimental frequencies and those calculated from Stark-effect theory.
The probabilities of single-photon 2s–1s transition in hydrogen (H) and antihydrogen ( Hˉ \bar H Hˉ ) atoms in an external electric field are calculated. These quantities are different for H and Hˉ \bar H Hˉ due to the presence of a T odd term linearly dependent on the electric field strength. The relative difference between the probabilities of the considered process for hydrogen and antihydrogen is given, and the conditions under which this difference can be measured are discussed.
The intensity of beam-foil-excited $\mathrm{Ly}\ensuremath{-}\ensuremath{\alpha}$ radiation has been measured in electric fields alternately parallel and antiparallel to the beam. Measurements were made at three energies---110, 165, and 210 keV---and three field strengths. From these data the $S\ensuremath{-}P$ co-herence term ${\ensuremath{\sigma}}_{\mathrm{SP}}$ has been determined. The magnitude of ${\ensuremath{\sigma}}_{\mathrm{SP}}$ is found to be 0.07 at 110 keV, 0.19 at 160 keV, and 0.22 at 210 keV. These results establish that beam-foil-excited hydrogen atoms have a nonzero electric dipole moment.
The interaction between a metastable H(2s) atomic hydrogen beam and an external electric field leads to the emission of the Lyman-α line. It originates in the Stark mixing of the near-degenerate 2s1/2 and 2p1/2 levels separated by the Lamb shift. The quenched radiation proportional to the square of the electric field amplitude is recovered in vacuum by using such an atomic probe beam. We observe the strong enhancement of the signal when the field is oscillating at the Lamb shift frequency. This technique is applied in a plasma, offering an alternative way to measure weak electric fields by direct and non-intrusive means.