We present the experimental evidence of the linear Stark behaviour in an atomic spectrum at low (absolute) electric field strengths on high lying quasi-hydrogenic series of atomic caesium. This is the behaviour which would be observed on hydrogen atoms for any level. It is exhibited here in the 1-15 V/cm range on quasi-hydrogenic atoms, excited, in vapour phase, by a c.w. dye laser to n = 60 Rydberg states. Under these conditions, the core effects are almost negligible compared with the first linear-in-field term in the Stark expansion of the energy.
This paper reports on the investigation of excitation spectra of rubidium Rydberg atoms in crossed electric and magnetic fields. The quasi-Landau spectra were evaluated and their Fourier transforms calculated. The scaled spectral scans used for this purpose were obtained by changing the electric and magnetic fields as well as the laser frequency in an appropriate way. The observed resonances could be explained completely by semiclassical orbits. Only orbits showing overlap with the ground-state wave function are observed. The polarization dependence of certain components in the Fourier spectra can be explained by the shape of the semiclassical orbits. The electric dipole moments of the atoms resulting from the shift of the quasi-Landau structures in a changing electric field agree quite well with the corresponding semiclassical orbits.
Calculations of the photoionisation of the lowest even- and odd-parity levels of atomic hydrogen in a magnetic field (10 3 <or=B<or=10 5 T) at photon energies from the ionisation threshold to 8 gamma Ryd above it are reported. The appropriate generalisation of the Wigner threshold law is given. Resonances are found at each embedded discrete continuum level and secondary maxima associated with the motion along the field are predicted, and confirmed analytically in a simple model. The results may be extended to any hydrogenic ion using a recent theorem of Wunner et al., which is quoted.
The Stark spectroscopy of the hydrogen atom has been investigated near the ionization threshold in static homogeneous external electric fields from \ensuremath{\sim}1000 to \ensuremath{\sim}8000 V/cm with use of a two-step excitation H(n=1)+\ensuremath{\Elzxh}${\ensuremath{\omega}}_{\mathrm{vuv}\ensuremath{\rightarrow}}$H(n=2)+\ensuremath{\Elzxh}\ensuremath{\omega} $_{\mathrm{uv}\ensuremath{\rightarrow}}$
H∗ with vuv and uv laser radiation, independently tunable and linearly polarized either parallel (\ensuremath{\pi}) or perpendicular (\ensuremath{\sigma}) with respect to the external field. Different from other, nonhydrogenic atoms, the hydrogen atom is a peculiar case insofar as the initial states of H(n=2), from which excitation takes place, are essentially of parabolic character at the field strengths employed in this study.Individual sublevels (
n1,
n2,\ensuremath{\Vert}
ml\ensuremath{\Vert}) have been prepared in the n=2 state with sub-Doppler resolution. Photoionization spectra have been obtained with \ensuremath{\pi}- and \ensuremath{\sigma}-polarized uv radiation from the four possible sublevels of the n=2 Stark manifold: \ensuremath{\Vert}1,0,0〉 \ensuremath{\Vert}\ifmmode\pm\else\textpm\fi{}1/2〉, \ensuremath{\Vert}0,1,0〉 \ensuremath{\Vert}\ifmmode\pm\else\textpm\fi{}1/2〉, \ensuremath{\Vert}0,0,\ifmmode\pm\else\textpm\fi{}1〉 \ensuremath{\Vert}\ifmmode\pm\else\textpm\fi{}1/2〉, and \ensuremath{\Vert}0,0,\ensuremath{\mp}1〉 \ensuremath{\Vert}\ifmmode\pm\else\textpm\fi{}1/2〉. All spectra show sharp line structures of quasistable field-ionizing states superimposed on continua in the energy region between the classical saddle point, ${E}_{\mathrm{SP}=\mathrm{\ensuremath{-}}2\phantom{\rule{0ex}{0ex}}\mathrm{\ensuremath{\surd}}\mathrm{F}}$ a.u., and the zero-field ionization threshold E=0 a.u. Employing existing theoretical treatments, the quasistable spectral structures are quantitatively completely analyzed and accounted for, as long as their field ionization rate is less than \ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}
1011 ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$. Field-ionization rates of quasistable states have been measured and are compared with theory. Oscillatory resonance structures of the ionization cross section near the zero-field threshold are observed with pronounced modulation degree only in the spectrum from the \ensuremath{\Vert}1,0,0〉 \ensuremath{\Vert}\ifmmode\pm\else\textpm\fi{}1/2〉 sublevel excited with the uv \ensuremath{\pi}-polarized. The energy spacing of the oscillations has been measured as a function of the electric field strength F and found to be nearly proportional to
F3/4, with slight but definite deviations. Theoretical analysis of the oscillations yields quantitative agreement with the experiment.
The Stark spectra of autoionizing Rydberg states of Xe converging to the second ionization limit 5
p5 2P1/2 have been investigated as a function of applied electric field over the range 26--2362 V/cm. Single-photon excitation from the Xe ground state was achieved using coherent radiation near 92.5 nm, generated by frequency tripling the pulsed output of a frequency-doubled dye laser in a free jet of rare-gas atoms. For the lowest electric field only the ns' and nd' series were observed. As the electric field was increased the np' series appeared because of the mixing of wave functions with different l values. Further increase of the electric field caused the appearance of hydrogenlike Stark manifolds. The Stark spectrum was simulated in a two-step procedure with no adjustable parameters. Using a jl-coupling basis set the Hamiltonian matrix was diagonalized to determine the energy levels and corresponding eigenfunctions for a given electric field strength. The intensities and line shapes were then calculated using the formalism developed by Fano for a many-discrete-level--single-continuum configuration interaction. This treatment was sufficient to reproduce the positions, widths, and shapes of most observed features. At field strengths between 1000 and 2000 V/cm, however, an additional modulation structure with a spacing of about 2.7 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ appeared on top of the \ensuremath{\Vert}M\ensuremath{\Vert}=1 autoionizing resonances, which could not be explained by our simple theoretical model.
Abstract We present a systematic densitometer mapping of diamagnetic effects on the principal series of Ba and Sr in absorption, with magnetic fields up to 4.7 T. The n- and l-mixing spectra are resolved in both σ- and π-polarization while the quasi-Landau resonances are observed near and above the ionization limit only in σ-polarization. Configuration interaction produces striking differences in the intensities and spacings of the n- and l-mixed spectra while only the shapes of the quasi-Landau resonances depend on the atomic systems.