Coherent Excitation ofSandPStates of then=2Term of Atomic Hydrogen

Abstract

1 An expression is given for the Stark-induced beat signal in the Lyman-o; radiation from hydrogen atoms in a beam-foil experiment. This expression includes possible contributions to the beat signal from coherent excitation of S and P 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.The recently developed beam-foil spectroscopic technique 1 has been used to investigate excited states of many atoms and ions. Among the most interesting results of these experiments have been the observations of periodic spatial fluctuations, or "beats/' in the intensity of the radiation emitted by light atoms and ions (H, He, Li + ) subsequent to their exit from the exciting foil. Since all the particles in the beam have nearly the same velocity, these spatial beats are equivalent to beats in time measured from the instant of excitation at the foil.Macek 2,3 has explained these temporal beats as the result of coherent excitation of neighboring fine-structure levels. With the beam direction as the axis of quantization, the symmetry of the experiment about this direction restricts the possibility of coherence to states of the same m ; . Further, the validity of Russell-Saunders coupling for these light atoms requires that only states of the same m L and m s can be coherently excited. Thus, beats between L Jttnj states with the same L and nij but different J (such as P 3/2 ,i/2 and Pi/g, i/ 2 ) ma Y more properly be thought of as the result of coherence induced by the fine-structure interaction (proportional to L • §) rather than the excitation process itself. 4 This is implicit in Macek's analysis 3 and has been explicitly stressed by Sellin. 5,6 Macek 3 has pointed out the possibility of beats between states with the same m ; but different L (such as S 1/2tl/2 beating with D 3/2tl/2 or 2> 5/2il/2 ). Such beats, which cannot be ruled out by any symmetry argument, require true coherence in the excitation process in the sense that the initial relative phases of these states averaged over successive atoms in the beam must not be totally random. There has been only one published report of the observation of such "true" coherence beats, that by Burns and Hancock. 7 In their beam-foil investigation of the Balmer-jS line of hydrogen, S-D beat signals appeared to be present along with fine-structure-induced beats between the P 3/2 and P 1/2 states and between the D 5/2 and D 3/2 states. Extraction of the amplitudes of the component signals required computer fitting of a rather complicated theoretical expression to the observed beat pattern. The purpose of the present Letter is to discuss coherent excitation contributions to the Stark-induced beat signal in the Lyman -a line of hydrogen. We shall show how these contributions can be separated experimentally from those resulting purely from cohe...

QED theory of the spectral line profile and its applications to atoms and ions

“…The latter problem was investigated in detail by many authors. We could mention, for example, the works of Maĉek [280] and Eck [281]. Both problems are connected with the influence of the neighboring levels on the characteristics of spectral lines.…”

“…The dimension of the matrices is determined by the number of the terms retained in Eq. (281). The evaluation of the positions of the resonances reduces to a task of solving of the eigenvalue problem.…”

“…E A 0 is the energy of the ground state. Within the resonance approximation we will have to retain two terms in the sum (281) corresponding to the basic functions Ψ (0) 1 (r 1 , r 2 ) and Ψ (0) 2 (r 1 , r 2 ). The scattering amplitude may be written as…”

Stark beats of Lyman-α emission of foil-excited hydrogen atom

“…Since Eck [1] has pointed out that odd-parity coherence has observable effects on the Ly-e photon emission when the hydrogen atom decays in an external electric field upon reversing the field direction, a series of observations have been reported. Soon after the Eck's proposal, two groups carried out the measurement on electric field induced modulations in the time decay of foil-excited hydrogen atom [2,3].…”

Coherent excitation of H(n=2) in H+, H - He collisions

“…Previous attempts to determine the full density matrix have investigated the field-induced Stark-beats or the field-dependent forward-backward asymmetry. A measurement of field-induced Stark-beats [8][9][10] requires a time-resolution of the order of 10-los. To our knowledge, the first such experiment was the work of Sellin et al [11], who established the existence of a nonzero asp after beam-foil excitation of H(n=2); the first complete density matrix for beam-foil excitation of H(n=2) was reported by Gaupp et al [-I2].…”