Stark-Induced Quantum Beats in H LY(alpha) Emission

Intensity beats in the emission of Ly(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 Psi(I, II) = alpha vertical bar p, 1/2, +/- 1/2 > + beta vertical bar s, 1/2 -/+ 1/2 > where vertical bar l, j, m(j)> notation and the beam as quantization axis are used. The ratio alpha/beta is then determined, which gives the ratio of the excitation cross section of the p to that of the s states as sigma(p)/sigma(s) >= 4 +/- 1 at a beam energy of 200 (keV) per atom.