Showing papers by "Stephan Fritzsche published in 2012"

Laser spectroscopy of radioactive isotopes: Role and limitations of accurate isotope-shift calculations

Abstract: Nuclear mean-square charge radii of radioactive isotopes are obtained from isotope-shift measurements using laser spectroscopy. To extract the values of $\ensuremath{\delta}\ensuremath{\langle}{r}^{2}\ensuremath{\rangle}$ the atomic field and mass shift factors need to be evaluated. We here summarize the currently available experimental and theoretical techniques for calculating the atomic field and mass shift factors for complex, open-shell atoms, including the $5{s}^{2}{\phantom{\rule{4pt}{0ex}}}^{1}\phantom{\rule{-0.16em}{0ex}}{S}_{0}\ensuremath{-}4d5p{\phantom{\rule{4pt}{0ex}}}^{1}\phantom{\rule{-0.16em}{0ex}}{P}_{1}$ and $4d5s{\phantom{\rule{4pt}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}{D}_{2}\ensuremath{-}4d5p{\phantom{\rule{4pt}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{1}$ transitions for singly charged yttrium ($Z=39$).

Mass- and field-shift isotope parameters for the 2s-2p resonance doublet of lithium-like ions.

Abstract: 1/2,3/2 transitions along the lithium isoelectronic sequence. Based on the multiconfiguration Dirac-Hartree-Fock method, the electron correlation and the Breit interaction are taken into account systematically. The analysis of the isotope shifts for these two transitions along the isoelectronic sequence demonstrates the importance and competition between the mass shifts and the field shifts.

Relativistic polarization analysis of Rayleigh scattering by atomic hydrogen

Abstract: A relativistic analysis of the polarization properties of light elastically scattered by atomic hydrogen is performed, based on the Dirac equation and second order perturbation theory. The relativistic atomic states used for the calculations are obtained by making use of the finite basis set method and expressed in terms of $B$ splines and $B$ polynomials. We introduce two experimental scenarios in which the light is circularly and linearly polarized, respectively. For each of these scenarios, the polarization-dependent angular distribution and the degrees of circular and linear polarization of the scattered light are investigated as a function of scattering angle and photon energy. Analytical expressions are derived for the polarization-dependent angular distribution which can be used for scattering by both hydrogenic as well as many-electron systems. Detailed computations are performed for Rayleigh scattering by atomic hydrogen within the incident photon energy range 0.5 to 10 keV. Particular attention is paid to the effects that arise from higher (nondipole) terms in the expansion of the electron-photon interaction.

Relativistic total cross section and angular distribution for Rayleigh scattering by atomic hydrogen

Abstract: We study the total cross section and angular distribution in Rayleigh scattering by hydrogen atom in the ground state, within the framework of Dirac relativistic equation and second-order perturbation theory. The relativistic states used for the calculations are obtained by making use of the finite basis set method and expressed in terms of B-splines and B-polynomials. We pay particular attention to the effects that arise from higher (non-dipole) terms in the expansion of the electron-photon interaction. It is shown that the angular distribution of scattered photons, while it is symmetric with respect to the scattering angle �=90 ◦ within the electric dipole approximation, becomes asymmetric when higher multipoles are taken into account. The analytical expression of the angular distribution is parametrized in terms of Legendre polynomials. Detailed calculations are performed for photons in the energy range 0.5 to 10 keV. When possible, results are compared with previous calculations.

Nuclear mean-square charge radii of 63,64,66,68-82 Ga nuclei: No anomalous behavior at N=32

Abstract: Collinear laser spectroscopy was performed on the ${}^{63,64,66,68\ensuremath{-}82}$Ga isotopes with neutron numbers from $N=32$ to $N=51$. These measurements were carried out at the ISOLDE radioactive ion beam facility at CERN. Here we present the nuclear mean-square charge radii extracted from the isotope shifts and, for the lighter isotopes, new spin and moment values. New ground-state nuclear spin and moments were extracted from the hyperfine spectra of ${}^{63,70}$Ga, measured on an atomic transition in the neutral atom. The ground-state spin of ${}^{63}$Ga is determined to be $I=3/2$. Analysis of the trend in the change in mean-square charge radii of the gallium isotopes demonstrates that there is no evidence of anomalous charge radii behavior in gallium in the region of $N=32$.

Photon Laser-Induced Fluorescence of Neutral Xenon in a Thin Xenon Plasma

Abstract: Two-photon absorption laser-induced fluorescence (TALIF) measurements of relative ground state densities of neutral xenon on the plume axis of the radio-frequency ion thruster RIT-10 are reported. ATALIF scheme involving excitation of the 6p0 1=2 0 was applied. TALIF signals have been analyzed both in the cold gas flow and during thruster operation. Results show the principle feasibility of the investigated TALIF scheme, which seems to be a useful extension to formerly applied TALIF transitions for diagnostics in a thin xenon plasma.

Formation of Kr3+ via core-valence doubly ionized intermediate states

Abstract: The time-of-flight photoelectron-photoion coincidence technique has been used to study single-photon 3d(9)4p(5) core-valence double ionization of Kr and subsequent Auger decay to triply charged sta ...

Electron emission from highly charged ions: signatures of magnetic interactions and retardation in strong fields

Abstract: The electron emission of highly charged ions has been reanalyzed with the goal of separating the magnetic and retardation contributions to the electron?electron (e?e) interaction from the static Coulomb repulsion in strong fields. A remarkable change in the electron angular distribution due to the relativistic terms in the e?e interaction is found, especially for the autoionization of beryllium-like projectiles, following a 1s???2p3/2 Coulomb excitation in collision with some target nuclei. For low-energetic, high-Z projectiles with Tp???10?MeV?u?1, a diminished (electron) emission in the forward direction as well as oscillations in the electron angular distribution due to the magnetic and retarded interactions are predicted for the autoionization of the 1s2s22p3/2 3P2 resonance into the 1s22s 2S1/2 ground and the 1s22p 2P1/2 excited levels of the finally lithium-like ions, and in contrast to a pure Coulomb repulsion between the bound and emitted electrons. The proposed excitation?autoionization process can be observed at existing storage rings and will provide a novel insight into the dynamics of electrons in strong fields.

Parametrization of the angular correlation and degree of linear polarization in two-photon decays of hydrogenlike ions

Abstract: The spontaneous two-photon emission in hydrogenlike ions is investigated within the framework of second-order perturbation theory and Dirac's equation. Special attention is paid to the angular correlation of the emitted photons as well as to the degree of linear polarization of one of the two photons, if the second is just observed under arbitrary angles. Expressions for the angular correlation and the degree of linear polarization are expanded in powers of cosine functions of the two-photon opening angle, whose coefficients depend on the atomic number and the energy sharing of the emitted photons. The effects of including higher (electric and magnetic) multipoles upon the emitted photon pairs beyond the electric-dipole approximation are also discussed. Calculations of the coefficients are performed for the transitions $2{s}_{1/2}\ensuremath{\rightarrow}1{s}_{1/2}$, $3{d}_{3/2}\ensuremath{\rightarrow}1{s}_{1/2}$, and $3{d}_{5/2}\ensuremath{\rightarrow}1{s}_{1/2}$, along the entire hydrogen isoelectronic sequence ($1\ensuremath{\le}Z\ensuremath{\le}100$).

Polarization correlations in radiative cascades following dielectronic recombination of high-Z ions

Abstract: We investigate the angular and polarization correlations between photons emitted in dielectronic recombination (DR) of initially hydrogen-like heavy ions. Computations are performed based on the density matrix approach and Dirac’s relativistic theory. Special attention is paid to the effects that arise from non-dipole terms in the expansion of the electron–photon interaction. To illustrate these effects, we present detailed calculations for the radiative cascades in K-LL DR of (initially) hydrogen-like uranium. Our computations show that the angle and polarization properties of the coincidently measured photons are significantly affected by a multipole-mixing between the leading electric-dipole (E1) and magnetic-quadrupole (M2) transitions. (Some figures may appear in colour only in the online journal)

Early onset of deformation in the neutron-deficient polonium isotopes

Abstract: In-source laser spectroscopy has been performed at CERN-ISOLDE with the RILIS laser ion source on 191–204,206,208–211,216,218Po. New information on the β decay of 199Po were extracted in the process, challenging previous results. Large-scale atomic calculations were performed to extract the changes in the mean-square charge radius δr2 from the isotope shifts. The δr2 for the even-A isotopes reveal a large deviation from the spherical droplet model for N < 116.

High-resolution optical spectroscopy of Os?with a view to laser cooling of atomic anions

Abstract: Atomic anions are generally not amenable to optical spectroscopy because they are loosely bound systems and rarely have bound excited states. Until recently, there was only one known negative ion with a strong bound–bound electronic transition, the osmium anion Os−. The electric-dipole transition between the 4Fe9/2 ground and 6DoJ excited state of this ion provides unique insight into the structure of atomic anions. In addition, it may enable the preparation of ultracold ensembles of negative ions. Laser excitation of the electric-dipole transition in Os− ions could be used to laser-cool them to microkelvin temperatures. If demonstrated to be successful, the technique would allow the cooling of any species of negatively charged ions - from subatomic particles to molecular anions - to ultracold temperatures by sympathetic cooling. We have been investigating the bound-bound electric-dipole transition in Os− by high-resolution laser spectroscopy with a view to using it for the first laser cooling of negative ions. The principle of the method, its potential applications, as well as experimental results are presented.

Angular distributions and correlations in sequential three-photon triple atomic ionization

Abstract: A theoretical description of the sequential three-photon triple atomic ionization is given within a model of stepwise ionization with emphasis on the angular distributions and angular correlations of the emitted electrons. The theory is applied to the photoionization of neon atom at 90.5 eV, corresponding to the experiment performed at the Free electron LASer in Hamburg (FLASH) by A. Rouzee et al (Phys. Rev. A 83 031401(R) (2011)).

Quantum correlations in the two-photon decay of few-electron ions

Abstract: The photon-photon polarization entanglement in the two-photon decay of metastable ionic states has been analyzed in the framework of the density matrix and second-order perturbation theory. Emphasis is placed especially upon the relativistic and non-dipole effects along the hydrogen- and helium-isoelectronic sequence.

Angular correlations in the sequential two-photon double ionisation of atomic xenon

Abstract: The sequential two-photon double ionization has been analyzed for the 4d electrons of atomic xenon in the region of the giant resonance and beyond (70–200 eV), for which intense FEL radiation is available at the free electron laser FLASH. The 4d vacancies in xenon couple strongly to the autoionization continuum with lifetimes of only a few fs, and their Auger decay thus competes with the subsequent (second-and higher-step) photoionization in typical FEL pulses.

Efficiency of the Eavesdropping in B92 QKD Protocol with a QCM

Abstract: Success of any eavesdropping attack on a quantum cryptographic protocol can be reduced by the legitime users if they partially compare their data. It is important to know for the legitime users what is (necessary and enough) amount of data which should be compared to ensure that (possible) illegitime user has an arbitrary small information about the rest of data. To obtain such amount the legitime users need to know efficiencies of all possible attacks for particular cryptographic protocol. In this work we introduce the eavesdropping attack on Bennett’s B92 protocol for quantum key distribution (QKD) with a quantum cloning machine (QCM). We demonstrate efficiency of suggested attack and compare it with efficiencies of alternative attacks proposed before.