Electron angular distributions and total cross sections for photoionisation of polarised Ne(3p3D3) atoms near threshold

Photoelectron angular distributions from autoionizing 4s¹4p⁶6p¹ states in atomic krypton probed with femtosecond time resolution

Photoelectron angular distributions (PADs) are obtained for a pair of 4s(1)4p(6)6p(1) (a singlet and a triplet) autoionizing states in atomic krypton. A high-order harmonic pulse is used to excite the pair of states and a time-delayed 801 nm ionization pulse probes the PADs to the final 4s(1)4p(6) continuum with femtosecond time resolution. The ejected electrons are detected with velocity map imaging to retrieve the time-resolved photoelectron spectrum and PADs. The PAD for the triplet state is inherently separable by virtue of its longer autoionization lifetime. Measuring the total signal over time allows for the PADs to be extracted for both the singlet state and the triplet state. Anisotropy parameters for the triplet state are measured to be β(2)=0.55 ± 0.17 and β(4)=-0.01 ± 0.10, while the singlet state yields β(2)=2.19 ± 0.18 and β(4)=1.84 ± 0.14. For the singlet state, the ratio of radial transition dipole matrix elements, X, of outgoing S to D partial waves and total phase shift difference between these waves, Δ, are determined to be X=0.56 ± 0.08 and Δ=2.19 ± 0.11 rad. The continuum quantum defect difference between the S and D electron partial waves is determined to be -0.15 ± 0.03 for the singlet state. Based on previous analyses, the triplet state is expected to have anisotropy parameters independent of electron kinetic energy and equal to β(2)=5∕7 and β(4)=-12∕7. Deviations from the predicted values are thought to be a result of state mixing by spin-orbit and configuration interactions in the intermediate and final states; theoretical calculations are required to quantify these effects.

Photoionization of synchrotron-radiation-excited atoms: separating partial cross sections by full polarization control

Resonant atomic excitation by synchrotron radiation and subsequent ionization by a tunable dye laser is used to study the photoionization of short-lived Rydberg states in Xe. By combining circular and linear polarization of the synchrotron as well as of the laser photons the partial photoionization cross sections were separated in the region of overlapping autoionizing resonances of different symmetry and the parameters of the resonances were extracted.

Determination of the phase difference between even and odd continuum wave functions in atoms through quantum interference measurements

We establish a technique for the determination of the phase difference between even and odd parity continuum wave functions in atoms. This determination is based upon our detailed measurements of a quantum mechanical interference between two photoionization processes using a two-color laser field. We present our measurement of the phase difference between the continuum p and d waves in atomic rubidium, which is in good agreement with the expected value.

Fine structure continuum cross section ratios in the two-photon ionization of rubidium using elliptically polarized light

Using fully relativistic perturbation theory we report fine structure continuum cross section ratios for the two-photon ionization of rubidium under elliptically polarized light. The choice of light polarization and wavelength matches the recent complete experiments on rubidium reported by Wang and Elliott [Phys. Rev. Lett. 84, 3795 (2000)]. The sigma(d5/2)/sigma(d3/2) cross section ratios calculated are consistent with results expected if relativistic fine structure effects are small, and are very much at odds with the recent experimental findings.

Determination of cross sections and continuum phases of rubidium through complete measurements of atomic multiphoton ionization

We present a complete experimental determination of the atomic parameters necessary to unambiguously characterize two-photon ionization of atomic rubidium, i.e., the relative photoionization cross sections and the continuum wave function phase difference. We obtain these complete results through a single measurement, that of the two-photon photoelectron angular distribution using elliptically polarized light. While measured phase differences are in excellent agreement with expected values, the ratios of photoionization cross sections of the two D channels are not.