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Journal of Physics B: Atomic, Molecular and Optical Physics invites you to submit a paper to a forthcoming special issue on Coherent Control to appear in 2008.

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Using the example of laser-assisted photoionization, we analyse the interplay of an intense laser field and the atomic/molecular potential during the electron motion after ionization. We give conditions to determine when the electron's oscillations in the strong laser field are approximately decoupled from its acceleration in the ionic potential, and when they are not. Excellent agreement between analytical and numerical results allows us to assess the recipes for analysing interference structures in high harmonic generation in molecules.

Interatomic resonant Auger can take place when the photon energy is tuned to a resonant core-level excitation of an atom neighbouring the emitting atom, with the emitting core-level having a lower binding energy than the resonant core-level. This phenomenon in a hetero-nuclear diatomic molecule has been demonstrated for the first time as the intensity enhancement of the lower core-level photoemission. Such a phenomenon should be considered to be general and then the present results in the simplest system open a door to a new horizon of photoemission studies for both isolated molecules and condensed systems including different atoms.

The excitation of a thin layer of two-level permanent dipole moment atoms by ultimately short (less than the field oscillation period) electromagnetic pulses (videopulse) is observed. The numerical analysis of the matter equations free of the rotating wave approximation and relaxation reveals a strong influence of the local field and the Stark effect on temporal behaviour of transmitted field. Specifically, it is demonstrated that a dense film irradiated by a videopulse emits a short response with a delay much longer even than the characteristic cooperative time of the atom ensemble. It is supposed that the local field in the thin layer of permanent dipole atoms is able to re-pump the atomic subsystem. A close analogy with nonlinear pendulum motion is discussed.

The importance of valence–shell, core–valence and core–core correlation and interactions between the members of 3s²nd ²D Rydberg series and between the Rydberg series and 3s3p²²D perturber state in singly ionized silicon has been examined using term-dependent non-orthogonal orbitals in the multiconfiguration Hartree–Fock approach. Large sets of spectroscopic and correlation non-orthogonal functions have been chosen to adequately describe the term dependence of wavefunctions, various correlation corrections and strong interactions in Rydberg series. The relativistic corrections are included through the one-body mass correction, Darwin and spin–orbit operators and two-body spin–other-orbit operator in the Breit–Pauli Hamiltonian. Extensive configuration-interaction wavefunctions have been used in the representation of Si II levels to calculate oscillator strengths and transition probabilities. The accuracy of present oscillator strengths is evaluated by the agreement between the length and velocity formulations combined with the agreement between the calculated and measured transition energies. The present results have been compared with previous calculations, experimental measurements and astronomical observations.

(e, 2e) ionization differential cross sections are presented for incident electron energies ranging from 15 eV to 95 eV above the ionization threshold of the 1b₁ molecular state of H₂O. Experimental results and theoretical analysis were derived for three energies in a coplanar symmetric geometry, and for three energies in an asymmetric geometry. The experimental data show a wide variation in the cross section over this range of energies, whereas the theoretical analysis carried out using a sophisticated molecular DWBA model, which includes the final state post collision interaction (PCI), shows best agreement at lower energies. The experimental techniques used to collect the data are described here as well as an improved theoretical approach using elastic scattering cross sections to evaluate the accuracy of the distorted waves utilized in the calculation of the ionization cross sections.

We report fully differential cross-section calculations using distorted wave theories for helium single ionization by 75 keV p impact. Comparisons are made with absolute experimental data and we find that good results are obtained in the magnitude without the need for normalization factors. However, discrepancies are quite apparent in the position and shape of the peak structures in the fully differential angular distribution of the ejected electrons. We assess the influence of the internuclear interaction on low-energy electron emission in the scattering plane and in the perpendicular plane. Our continuum distorted wave-eikonal initial state calculations with (without) the internuclear interaction yield better results for the large (small) momentum transfer. We discuss this behaviour as a consequence of active electron screening for low-energy electron emission.

We study the properties of excited states of an array of weakly coupled quasi-two-dimensional Bose condensates using hydrodynamic theory. We calculate the multibranch Bogoliubov–Bloch spectrum and its corresponding eigenfunctions. The spectrum of the axial excited states and its eigenfunctions strongly depends on the coupling among various discrete radial modes within a given symmetry. This mode coupling is due to the presence of a radial trapping potential. The multibranch nature of the Bogoliubov–Bloch spectrum and its dependence on the mode coupling can be realized by analysing the dynamic structure factor and momentum transferred to the system in Bragg spectroscopy experiments. We also study the dynamic structure factor and momentum transferred to the condensate due to the Bragg spectroscopy experiment.

We report on molecular frame angular distributions of 2s photoelectrons and electrons emitted by interatomic Coulombic decay from neon dimers. We found that the measured angular distribution of the photoelectron strongly depends on the environment of the cluster. The experimental results are in excellent agreement with frozen core Hartree–Fock calculations. The ICD electrons show slight variations in their angular distribution for different kinetic energies.

The dynamics of dissociation of pre-ionized D⁺₂ molecules using intense (10¹²–10¹⁵ W cm⁻²), ultrashort (50 fs), infrared (λ = 790 nm) laser pulses are examined. Use of an intensity selective scan technique has allowed the deuterium energy spectrum to be measured over a broad range of intensity. It is found that the dominant emission shifts to lower energies as intensity is increased, in good agreement with corresponding wavepacket simulations. The results are consistent with an interpretation in terms of bond softening, which at high intensity (approximately >3 × 10¹⁴ W cm⁻²) becomes dominated by dissociative ionization. Angular distribution measurements reveal the presence of slow molecular dissociation, an indication that vibrational trapping mechanisms occur in this molecule.

For one-dimensional vibrating cavity systems appearing in the standard illustration of the dynamical Casimir effect, we propose an approach to the construction of exact closed-form solutions. As new results, we obtain solutions that are given for arbitrary frequencies, amplitudes and time regions. In a broad range of parameters, a vibrating cavity model exhibits the general property of exponential instability. Marginal behaviour of the system manifests in a power-like growth of radiated energy.

An irreversible time evolution of a quantum system interacting with a surrounding environment is described by a quantum master equation. When an external field is applied to a quantum system, a non-Markovian master equation is derived in a rigorous way, where the relaxation terms in the quantum master equation include the effect of the external field that is ignored in the conventional treatment. It is shown that when the external field is a sequence of phase-modulation π-pulses, the decoherence of the quantum system can be suppressed. In particular, when the pulse separation is sufficiently short in comparison with the correlation time of the environmental system, dynamical decoupling takes place. To see the effect of the phase-modulation π-pulses, the time evolution of qubit entanglement is investigated in detail.

We examine the spin asymmetry of ground states for two-dimensional, harmonically trapped two-component gases of fermionic atoms at zero temperature with weakly repulsive short-range interactions. Our main result is that, in contrast to the three-dimensional case, in two dimensions a non-trivial spin-asymmetric phase can only be caused by the shell structure. A simple, qualitative description is given in terms of an approximate single-particle model, comparing well to the standard results of Hartree–Fock or direct diagonalization methods.

Effective potentials of the relativistic mα⁶ order correction for the ground state of the Coulomb two-centre problem are calculated. They can be used to evaluate the relativistic contribution of that order to the energies of hydrogen molecular ions or metastable states of the antiprotonic helium atom, where precision spectroscopic data are available. In our studies we use the variational expansion based on randomly chosen exponents that permits us to achieve high numerical accuracy.

In this paper, we formulate a quantum jump approach associated with single fluorescent systems whose radiative decay is defined by a Lindblad-like equation with a memory kernel. We base our results in a generalized Born–Markov approximation, which allows us to get our results from a full microscopic description. In the weak-laser-excitation regime, the photon-emission process can be described through a delay function, which in a natural way provides the basis for unravelling the dynamics in terms of a stochastic density matrix. As in the Markovian case, the stochastic dynamics consists in periods where the evolution is smooth and non-unitary, interrupted at random times where the photon-detection events produce a sudden change in the system state. The phenomenon of non-Poissonian intermittent fluorescence induced by complex environments (Budini 2006 Phys. Rev. A 73 061802) is analysed in the context of this approach.

We propose a simple and pedagogical wavefunction for the ground state of two-electron atoms which (i) is parameter free, (ii) satisfies all two-particle cusp conditions, (iii) yields reasonable ground-state energies, including the prediction of a bound state for H⁻. The mean energy, and other mean physical quantities, is evaluated analytically. The simplicity of the result can be useful as an easy-to-use wavefunction when testing collision models.

We consider Feshbach scattering of fermions in a one-dimensional optical lattice. By formulating the scattering theory in the crystal momentum basis, one can exploit the lattice symmetry and factorize the scattering problem in terms of centre-of-mass and relative momentum in the reduced Brillouin zone scheme. Within a single-band approximation, we can tune the position of a Feshbach resonance with the centre-of-mass momentum due to the non-parabolic form of the energy band.

Based on inverse kinematics the close relation between radiative electron capture to the projectile continuum, calculated within the impulse approximation, and electron–nucleus bremsstrahlung is shown. Particular emphasis is laid on the short-wavelength limit corresponding to cusp-electron emission in the target frame of reference. Differential cross sections and the degree of photon polarization are calculated for the coincident emission of electron and photon. Coplanar and non-coplanar geometries are considered, and the polarization is compared with that obtained from experiments on the elementary bremsstrahlung process and on radiative electron capture to bound states.

Measurements of x-ray line intensities following the decay of atomic vacancies produced in the L₃ subshell of dysprosium and holmium have been carried out. A filtered x-ray generator beam obtained by filters based on the K-edges of suitable elements combined with low-Z element filters has been used to selectively ionize the L₃ subshells. Fluorescence yields ω₃ and partial radiative width ratios have been extracted and compared with previous measurements and with theoretical and/or semi-empirical values from the literature. An overall good agreement has been obtained. The possibility of extending these measurements to other subshells is briefly outlined.

Two atomic models of the population dynamics of substates within the n = 4 and n = 3 multiplets of nickel-like tungsten and beryllium-like iron, respectively, are described in this paper. The flexible atomic code (FAC) is used to calculate the collisional and radiative couplings and energy levels of the excited states within these ionization stages. These atomic models are then placed within larger principal-quantum-number-based ionization dynamic models of both tungsten and iron plasmas. Collisional-radiative equilibrium calculations are then carried out using these models that demonstrate how the multiplet substates depart from local thermodynamic equilibrium (LTE) as a function of ion density. The effect of these deviations from LTE on the radiative and collisional deexcitation rates of lumped 3s, 3p, 3d, 4s, 4p, 4d and 4f states is then calculated and least-squares fits to the density dependence of these lumped-state rate coefficients are obtained. The calculations show that, with the use of lumped-state models (which are in common use), one can accurately model the L- and M-shell ionization dynamics occurring in present-day Z-pinch experiments only through the addition of these extra, non-LTE-induced, rate coefficient density dependences. However, the derivation and use of low-order polynomial fits to these density dependences makes lumped-state modelling both viable and of value for post-processing analyses.

A high-resolution threshold photoelectron spectrum of Xe was measured in the photon energy region of the 5s²5p⁴nl states. The peak width of the measured Xe 5s⁻¹ main line was close to 5 meV. A previously measured spectrum of Kr was also analysed. Rich satellite peaks were clearly observed, including many peaks not observed in previous optical, photoelectron and threshold photoelectron studies. The satellite peak energies and their assignments for Kr and Xe are listed. The observed Rydberg series converging to the Xe²⁺ ground state was assigned to the (³P₂)ng series by detailed analysis. The energy level of the Xe^{2+ 3}P₂ state as the converging limit of the observed Rydberg series was obtained as 38.355 eV.

A series of precise measurements of the hyperfine structure (hfs) of nine metastable levels in a chromium atom ⁵³Cr has been performed. For eight levels the hfs has been investigated with the method of laser induced fluorescence (LIF) on an atomic beam, and for the lowest-lying metastable level 3d⁵4s ⁵S₂ a still more precise method of laser-rf double resonance on an atomic beam (ABMR-LIRF) has been applied. A semi-empirical analysis of the fine and the hyperfine structure of the chromium atom, including many-body interaction effects, has been carried out in order to determine the value of the nuclear electric quadrupole moment, which amounts to Q = −0.22(1) barn.