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Physical Review Letters

Zero-Field Quantum Beats Subsequent to Beam-Foil Excitation

H. J. Andrä

Published Aug 10, 1970• 115 citations
Publisher

Abstract

The creation of ${M}_{L}$ alignment due to the foil excitation process is demonstrated with the observation of zero-field quantum beats in He $3^{3}P\ensuremath{-}2^{3}S$ 3880-\AA{}, hydrogen ${\mathrm{H}}_{\ensuremath{\alpha}}$, and hydrogen ${\mathrm{H}}_{\ensuremath{\beta}}$ emission.

DOI
10.1103/physrevlett.25.325

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The creation of ML{M}_{L}ML​ alignment due to the foil excitation process is demonstrated with the observation of zero-field quantum beats in He 33P\ensuremath−23S3^{3}P\ensuremath{-}2^{3}S33P\ensuremath−23S 3880-\AA{}, hydrogen H\ensuremathα{\mathrm{H}}_{\ensuremath{\alpha}}H\ensuremathα​, and hydrogen H\ensuremathβ{\mathrm{H}}_{\ensuremath{\beta}}H\ensuremathβ​ emission.
Zero-field quantum beats were observed in $\mathrm{L}\mathrm{y}\ensuremath{-}\ensuremath{\beta}$ emission (1026 \AA{}) from hydrogen atoms formed by beam-foil excitation, and the energy dependence of the magnetic-substate cross sections for n=3n=3n=3, l=1l=1l=1 states was determined for beam energies in the range from 230 to 500 keV/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,mj〉|l,j,{m}_{j}〉∣l,j,mj​〉 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 ppp to that of the sss 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.