Physical Review Letters

Zero-Field Intensity Oscillations Following Impulsive Excitation of Hydrogen

Donal J. Burns, Walter H. Hancock

Published Aug 16, 1971• 45 citations

Abstract

In a beam-foil experiment, we have observed zero-field oscillations of approximately 25% in the intensity of ${\mathrm{H}}_{\ensuremath{\beta}}$ radiation polarized parallel to the beam. An unmodulated decay is observed when a signal proportional to the total intensity is examined. Our observations substantiate Macek's theory of coherent decay from fine-structure levels.

DOI: 10.1103/physrevlett.27.370

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Physical Review LettersFeb 11, 197469 citations

Physical Review Letters

Zero-Field Intensity Oscillations Following Impulsive Excitation of Hydrogen

Donal J. Burns, Walter H. Hancock

Published Aug 16, 1971• 45 citations

Publisher

Abstract

In a beam-foil experiment, we have observed zero-field oscillations of approximately 25% in the intensity of

{\mathrm{H}}_{\ensuremath{\beta}}

radiation polarized parallel to the beam. An unmodulated decay is observed when a signal proportional to the total intensity is examined. Our observations substantiate Macek's theory of coherent decay from fine-structure levels.

DOI: 10.1103/physrevlett.27.370

Related papers

Interference Between Coherent Emissions in the Measurement of Atomic Lifetimes

J. H. Macek

Physical Review LettersJul 7, 196974 citations

Relative Orbital and Magnetic Substate Amplitudes in Single-Foil Excitation of Fast Hydrogen Atoms

I. A. Sellin, John A. Biggerstaff, P. M. Griffin

Within the limits set by our experimental apparatus, large-amplitude zero-field oscillations of H fine-structure amplitudes treated in a recent letter of Macek were not observed in polarization---versus---flight-path measurements on ${\mathrm{H}}_{\ensuremath{\beta}}$, ${\mathrm{H}}_{\ensuremath{\gamma}}$, and ${\mathrm{Ly}}_{\ensuremath{\alpha}}$ emissions from suddenly excited H atoms (50- and 150-keV incident protons). Random initial phases for orbital and magnetic substates and approximately equal magnetic substate populations are indicated, in contrast to binary electron capture in gases. A successful test of the theoretical polarization of $2s$ Stark quench radiation was also made.Within the limits set by our experimental apparatus, large-amplitude zero-field oscillations of H fine-structure amplitudes treated in a recent letter of Macek were not observed in polarization---versus---flight-path measurements on ${\mathrm{H}}_{\ensuremath{\beta}}$, ${\mathrm{H}}_{\ensuremath{\gamma}}$, and ${\mathrm{Ly}}_{\ensuremath{\alpha}}$ emissions from suddenly excited H atoms (50- and 150-keV incident protons). Random initial phases for orbital and magnetic substates and approximately equal magnetic substate populations are indicated, in contrast to binary electron capture in gases. A successful test of the theoretical polarization of $2s$ Stark quench radiation was also made.

Physical Review AAug 1, 197037 citations

Stark-Induced Quantum Beats in H L Y α Emission

H. J. Andrä

Intensity beats in the emission of $\mathrm{L}{\mathrm{y}}_{\ensuremath{\alpha}}$ from beam-foil excited hydrogen in various static electromagnetic field configurations have been studied. The observed beat frequencies agree with the calculated values, which are independent of the field directions. The beat amplitudes, however, show significant dependence on the field directions relative to the beam. The theory for emission of light from the decay of coherently excited states is applied in the sudden perturbation limit. Agreement with experiment can only be obtained under the assumption that the foil excitation generates initial coherent wave functions ${\ensuremath{\Psi}}_{\mathrm{I},\mathrm{I}\mathrm{I}}=\ensuremath{\alpha}|p,\frac{1}{2},\ifmmode\pm\else\textpm\fi{}\frac{1}{2}〉+\ensuremath{\beta}|s,\frac{1}{2},\ensuremath{\mp}\frac{1}{2}〉$, where $|l,j,{m}_{j}〉$ notation and the beam as quantization axis are used. The ratio $\frac{\ensuremath{\alpha}}{\ensuremath{\beta}}$ is then determined, which gives the ratio of the excitation cross section of the $p$ to that of the $s$ states as $\frac{{\ensuremath{\sigma}}_{p}}{{\ensuremath{\sigma}}_{s}}>~4\ifmmode\pm\else\textpm\fi{}1$ at a beam energy of 200 (keV) per atom.Intensity beats in the emission of $\mathrm{L}{\mathrm{y}}_{\ensuremath{\alpha}}$ from beam-foil excited hydrogen in various static electromagnetic field configurations have been studied. The observed beat frequencies agree with the calculated values, which are independent of the field directions. The beat amplitudes, however, show significant dependence on the field directions relative to the beam. The theory for emission of light from the decay of coherently excited states is applied in the sudden perturbation limit. Agreement with experiment can only be obtained under the assumption that the foil excitation generates initial coherent wave functions ${\ensuremath{\Psi}}_{\mathrm{I},\mathrm{I}\mathrm{I}}=\ensuremath{\alpha}|p,\frac{1}{2},\ifmmode\pm\else\textpm\fi{}\frac{1}{2}〉+\ensuremath{\beta}|s,\frac{1}{2},\ensuremath{\mp}\frac{1}{2}〉$, where $|l,j,{m}_{j}〉$ notation and the beam as quantization axis are used. The ratio $\frac{\ensuremath{\alpha}}{\ensuremath{\beta}}$ is then determined, which gives the ratio of the excitation cross section of the $p$ to that of the $s$ states as $\frac{{\ensuremath{\sigma}}_{p}}{{\ensuremath{\sigma}}_{s}}>~4\ifmmode\pm\else\textpm\fi{}1$ at a beam energy of 200 (keV) per atom.

Physical Review ADec 1, 197042 citations

Interference of Fine-Structure Levels of He ii

William S. Bickel, STANLEY BASHKIN

Passage of a beam of foil-excited ${\mathrm{He}}^{+}$ ions through a small electric field induced quasiperiodic fluctuations in the intensity of the light emitted from levels $n=7, 8, 9, \mathrm{and} 10$ . Both ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{4}$ beams were used. Only one foil was needed, in contrast to the double-foil arrangement reported necessary for hydrogen. The observations are discussed in terms of Stark-induced interference of the fine-structure levels of He ii, but discrepancies between the data and the calculations are large.Passage of a beam of foil-excited ${\mathrm{He}}^{+}$ ions through a small electric field induced quasiperiodic fluctuations in the intensity of the light emitted from levels $n=7, 8, 9, \mathrm{and} 10$. Both ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{4}$ beams were used. Only one foil was needed, in contrast to the double-foil arrangement reported necessary for hydrogen. The observations are discussed in terms of Stark-induced interference of the fine-structure levels of He ii, but discrepancies between the data and the calculations are large.

Physical ReviewOct 5, 196731 citations

Electric-Field and Multiple-Foil Excitation Experiments on Beam-Foil-Excited Hydrogen Atoms*

William S. Bickel

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.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.

Journal of the Optical Society of AmericaFeb 1, 196832 citations

Measurement of S−P Coherence in the Beam-Foil—Excited n=2 State of Atomic Hydrogen

Andreas Gaupp, H. J. Andrä, J. H. Macek

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 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.

Physical Review LettersFeb 11, 197469 citations

In a beam-foil experiment, we have observed zero-field oscillations of approximately 25% in the intensity of

{\mathrm{H}}_{\ensuremath{\beta}}

2s

Stark quench radiation was also made.

|l,j,{m}_{j}〉

notation and the beam as quantization axis are used. The ratio $\frac{\ensuremath{\alpha}}{\ensuremath{\beta}}$ is then determined, which gives the ratio of the excitation cross section of the

p

to that of the

s

states as $\frac{{\ensuremath{\sigma}}_{p}}{{\ensuremath{\sigma}}_{s}}>~4\ifmmode\pm\else\textpm\fi{}1$ at a beam energy of 200 (keV) per atom.

Passage of a beam of foil-excited

{\mathrm{He}}^{+}

ions through a small electric field induced quasiperiodic fluctuations in the intensity of the light emitted from levels

n=7, 8, 9, \mathrm{and} 10

. Both

{\mathrm{He}}^{3}

and

{\mathrm{He}}^{4}

beams were used. Only one foil was needed, in contrast to the double-foil arrangement reported necessary for hydrogen. The observations are discussed in terms of Stark-induced interference of the fine-structure levels of He ii, but discrepancies between the data and the calculations are large.