Double ionization of He(1s2) and He(1s2s 3S) by a single high-energy photon

QUANTUM INTERFERENCE AND LASER PULSE PHASE EFFECT ON THE PHOTOIONIZATION RATES OF EXCITED HYDROGEN ATOMS IN THE TUNNELING REGION

Using the generalized Keldysh theory, we investigate the quantum interference and the laser pulse phase effects by tunneling photoionization of an excited hydrogen atom. We assume that its initial state be a linear combination of 1s, 2s, 2p Stark-shifted atomic states. It is found that within the Keldysh approximation, quantum interference can take place among the 1s, 2s, and 2pz states, while this is not the case among 1s, 2s, 2pz and 2px, 2py, or 2px and 2py themselves. From the numerical calculations, we predict that the prominent destructive quantum interference takes place between 2s and 2pz atomic orbitals. In addition, we have found that in general, the laser pulse phase does not affect the individual photoionization rates while it does affect the quantum interference terms.

Controlling two-electron threshold dynamics in double photoionization of lithium by initial-state preparation

Double photoionization (DPI) and ionization-excitation (IE) of Li(2s) and Li(2p), state-prepared and aligned in a magneto-optical trap, were explored in a reaction microscope at the free-electron laser in Hamburg (FLASH). From 6 to 12 eV above threshold (homega = 85, 91 eV), total as well as differential DPI cross sections were observed to critically depend on the initial state and, in particular, on the alignment of the 2p orbital with respect to the VUV-light polarization, whereas no effect is seen for IE. The alignment sensitivity is traced back to dynamical electron correlation at threshold.

Mechanisms of photo double ionization of helium by 530 eV photons

We have measured fully differential cross sections for photo double ionization of helium 450 eV above the threshold. We have found an extremely asymmetric energy sharing between the photoelectrons and an angular asymmetry parameter beta approximately 2 and beta approximately 0 for the fast and slow electrons, respectively. The electron angular distributions show a dominance of the shakeoff for 2 eV electrons and clear evidence of an inelastic electron-electron scattering at an electron energy of 30 eV. The data are in excellent agreement with convergent close-coupling calculations.