Table of contents

The emission spectrum of neodymium produced by vacuum spark sources was observed in the vacuum ultraviolet on two normal-incidence spectrographs. In an initial result, more than 550 lines have been identified as transitions from 85 4f²5d levels to 37 levels of the 4f³ ground configuration in the free ion Nd³⁺. The levels 4f³⁴F_3/2 and ⁴I_11/2, responsible for the well-known 1064 nm laser line, have respective positions of 11 698.57 ±0.1 cm⁻¹ and 1897.07 ±0.1 cm⁻¹ above the ground level ⁴I_9/2. The newly found levels of 4f³ constitute the first isolated 4f^N configuration (N > 2) and therefore enable checks of effective parameters that represent far configuration interaction. Slater parameters F^k(4f, 4f) derived from Nd³⁺:LaCl₃ are 3% to 5% smaller than in the free ion.

With MgH⁺ ions as a test case, we investigate to what extent the rotational motion of smaller polar molecular ions sympathetically cooled into Coulomb crystals in linear Paul traps couples to the translational motions of the ion ensemble. By comparing the results obtained from rotational resonance-enhanced multiphoton photo-dissociation experiments with data from theoretical simulations, we conclude that the effective rotational temperature exceeds the translational temperature (<100 mK) by more than two orders of magnitude, indicating a very weak coupling.

We present classical trajectory Monte Carlo (CTMC) calculations of total and partial cross sections for capture and ionization in Ar¹⁸⁺, Ar¹⁷⁺, Ar¹⁶⁺+H(1s) collisions in the 30–300 keV amu⁻¹ impact energy range. We specially focus on capture into high-lying states of the projectile, which are of paramount importance for diagnostics of fusion plasmas involving Ar^q+ seeding.

Solving the full classical four-body Coulomb problem numerically using a Wigner initial distribution, we formulate a classical-quantum hybrid approach to study triple ionization by single photon absorption from the Li ground state in the threshold region. We confirm the Wannier threshold law σ ∝ E^α, and we show that α determined in the interval between 2 and 5 eV deviates from the analytical threshold value of 2.16 which we find in the interval between 0.1 and 2 eV.

This review covers the outer core level photoionization of the free 3d metal atoms from Sc to Cu. The experimental 3p, 3s and 2p photoemission and photoabsorption spectra are discussed. A comparison emphasizes common features and distinct differences. The interpretation of the data based on ab initio calculations reveals the influence of multi-electron interactions in the 3d metal atoms. We focus on the fundamental effects and main interactions which govern the electronic structure of these open shell atoms.

We present the first experimental demonstration of the optical Sagnac effect at the single-photon level. Using a high quality guided-wave heralded single-photon source at 1550 nm and a fibre optics setup, we obtain an interference pattern with net visibilities up to (99.2 ± 0.4%). On the basis of this high visibility and the compactness of the setup, the interest of such a system for fibre optics gyroscope is discussed.

Two different experimental methods, namely threshold electron–Auger electron coincidences and slow photoelectron–Auger electron coincidences are applied to investigate the Xe 4d Auger decay in the near-threshold region and reveal the essential role of electron correlation. The coincidences allow us to select the different channels for the 4d hole Auger decay which lead to different final states of the Xe²⁺ ion: 5s⁻²(¹S₀), 5s⁻¹5p⁻¹(¹P₁), 5p⁻²(¹S₀), 5p⁻²(¹D₂), 5p⁻²(³P_0,1) and 5p⁻²(³P₂). Measurements of the threshold electrons with the first method reveal strong PCI distortion of electron spectra in all channels. Comparison with calculations carried out in the framework of the quantum-mechanical PCI model allows us to clarify the dynamics of threshold electron production. In the 5p⁻²(¹S₀) channel, the main contribution comes from the PCI retardation of slow photoelectrons. In the 5p⁻²(¹D₂) and 5p⁻²(³P) final state channels, additional processes of PCI recapture followed by valence multiplet decays play a role at and below the N₄ and N₅ thresholds. The slow photoelectron spectra measured by the second method reveal also a strong PCI distortion. Analysis within the framework of the eikonal model shows the influence of the Auger electron on the PCI distorted line shapes.

We studied the multielectron ionization and Coulomb explosion of O₂ irradiated by 110 fs, 810 nm laser pulses at an intensity of 10¹⁵ W cm⁻². Strong anisotropic angular distributions with the same widths were observed for the atomic ions Oⁿ⁺ (n = 1–3). Using two linearly polarized laser pulses with crossed polarization, we found that the atomic ions generated in the second laser pulse were strongly depleted by the first laser pulse for various delay times. The results demonstrate that dynamic alignment dominates for O₂ under the experimental conditions. Moreover, the same angular distributions for all the atomic ions Oⁿ⁺ (n = 1–3) further demonstrate that dynamic alignment mainly occurs at the rising edge of the laser pulse with laser intensity below the ionization threshold and the neutral O₂ aligns along the laser polarization vector prior to ionization.

We report the extension of a model, based on geometrical optics, that was developed to explain similarities found in the cross sections of electron collisions with small hydrocarbons. Here we discuss the modifications made in the model and apply it to electron-collisions with molecules containing other atoms besides carbon and hydrogen. We then apply the model to predict the cross sections for the larger molecules C₆H₆, C₈H₈, C₆₀ and C₆F₆, and find that, even in this case, the model is useful for a first estimate of the theoretically calculated and experimental elastic cross sections.

We propose the realization of custom-designed adiabatic potentials for cold atoms based on multimode radio frequency radiation in combination with static inhomogeneous magnetic fields. For example, the use of radio frequency combs gives rise to periodic potentials acting as gratings for cold atoms. In strong magnetic field gradients, the lattice constant can be well below 1 µm. By changing the frequencies of the comb in time the gratings can easily be propagated in space, which may prove useful for Bragg scattering atomic matter waves. Furthermore, almost arbitrarily shaped potentials are possible such as disordered potentials on a scale of several 100 nm or lattices with a spatially varying lattice constant. The potentials can be made state selective and, in the case of atomic mixtures, also species selective. This opens new perspectives for generating tailored quantum systems based on ultracold single atoms or degenerate atomic and molecular quantum gases.

We study a class of laser cooling schemes that combine velocity-selective coherent population trapping (VSCPT) with Doppler cooling mechanisms. The Doppler mechanism prevents the atoms from diffusing into the region of high momentum, thereby removing the characteristic long-time asymptotic behaviour of VSCPT where, in the end, all the atoms escape from the trap. It is shown that the transition J_g = 2 to J_e = 1 while maintaining the simple field configuration present in the original VSCPT case provides the additional Doppler mechanism and leads to virtually zero temperature without the loss of atoms that characterize the original VSCPT dynamics.

Adiabatic passage with optical pulses has been used as an efficient tool for the transfer of atomic populations between Zeeman sublevels. The composition of the final state after adiabatic passage is investigated in the context of applications to atomic fountain frequency standards. Theoretical and experimental studies on the influence of the purity of the initial state on the result of the transfer are presented. Similarly, the role of the quality of polarization of the laser pulses in the process of adiabatic passage is discussed.

In this work we present fully differential cross sections (FDCSs) calculations using post and prior versions of CDW–EIS theory for helium single ionization by 100 MeV C⁶⁺ amu⁻¹ and 3.6 MeV amu⁻¹ Au²⁴⁺ and Au⁵³⁺ ions. We performed our calculations for different momentum transfer and ejected electron energies. The influence of internuclear potential on the ejected electron spectra is taken into account in all cases. We compare our calculations with absolute experimental measurements. It is shown that prior version calculations give better agreement with experiments in almost all studied cases.

Photon-induced fluorescence spectroscopy has been used to study the fragmentation of the water molecule at the O 1s edge. Fluorescence emission has been observed from the neutral fragments H, O and OH as well as from the ionic fragments O⁺ and OH⁺. The extracted fluorescence yields of the H Lyman-α emission and O 2p³(⁴S)3p(³P) → 2p³(⁴S)3s(³S) transitions show the same structures as the total ion yield spectrum but with different relative intensities. The most intense fluorescence emission is restricted to the region of the core excitations, while above the O 1s ionization limit the signal is much weaker (in the case of H) or below the detection limit (O, OH and OH⁺). The fluorescence emission is concluded to follow from the following general cascade: the core-excited states decay by resonant Auger transitions, the final states reached undergo dissociation into ionic and neutral fragments, and fluorescence occurs from excited fragments. In the case of the OH (A²Σ⁺ → X²Π) emission, the decay of core-excited states through soft x-ray emission may also be responsible for the observed fluorescence.

We study the revival and fractional revivals of a diatomic molecular wave packet of circular states whose weighing coefficients are peaked about a vibrational quantum number and a rotational quantum number . Furthermore, we show that the interplay between the rotational and vibrational motion is determined by a parameter , where D is the dissociation energy and C is inversely proportional to the reduced mass of the two nuclei. Using I₂ and H₂ as examples, we show, both analytically and visually (through animations), that for , the rotational and vibrational time scales are so far apart that the ro-vibrational motion gets decoupled and the revival dynamics depends essentially on one time scale. For , on the other hand, the evolution of the wave packet depends crucially on both the rotational and vibrational time scales of revival. In the latter case, an interesting rotational–vibrational fractional revival is predicted and explained.

Influences of an asymmetric noisy quantum channel on continuous variable entanglement and quantum teleportation are investigated. It is shown that when the resource of entanglement is a two-mode squeezed-vacuum state, the amount of the shared entanglement and the performance of the quantum teleportation are greater (smaller) in the symmetric quantum channel than in the asymmetric one if , where and are the average photon numbers of the two-mode squeezed-vacuum state and the thermal noise. When the quantum teleportation is carried out in the asymmetric quantum channel, introducing an additional loss makes better the performance of the quantum teleportation under certain conditions. The introduction of an additional loss makes smaller not only the shared entanglement but also the degree of the channel asymmetry.

Since the introduction of higher order nonclassical effects, higher order squeezing has been reported in a number of different physical systems but higher order antibunching is predicted only in three particular cases. In the present work, we have shown that the higher order antibunching is not a rare phenomenon; rather it can be seen in many simple optical processes. To establish our claim, we have shown it in the six wave mixing process, four wave mixing process and second harmonic generation process.

We have analysed the properties of an electromagnetically induced grating formed in a Ξ-type three-level atomic system in the presence of a standing wave pump and travelling wave probe fields at resonant and off-resonant two-photon absorption. We have also shown the validity of this grating in an inhomogeneously broadened regime.

We study the evolution of a trapped atomic cloud subject to a trapping frequency jump for two cases: stationary and moving centre of mass. In the first case, the frequency jump initiates oscillations in the cloud's momentum and size. At certain times we find the temperature is significantly reduced. When the oscillation amplitude becomes large enough, local density increases induced by the anharmonicity of the trapping potential are observed. In the second case, the oscillations are coupled to the centre-of-mass motion through the anharmonicity of the potential. This induces oscillations with even larger amplitudes, enhancing the temperature reduction effects and leading to nonisotropic expansion rates while expanding freely.

Predictions about the shapes of the K x-ray spectra of medium-Z and heavy atoms have been made on the basis of the results of theoretical multiconfiguration Dirac–Fock calculations (with the inclusion of the transverse Breit interaction and QED corrections) for various KL⁰M¹ x-ray satellite lines of Pd, Tb, Ta and Th. The construction of theoretical stick and synthesized (the sum of the Lorentzian natural line shapes) K x-ray spectra (including also diagram and KL¹M⁰ satellite lines) has enabled foreseeing such details of experimental spectra as the overlapping and visibility of particular groups of lines. The energy regions possibly best for the extraction of the satellite contributions in the measured K x-ray spectra have been indicated for each studied element. The effect of additional single ionization of the different subshells of the M shell on the structure and shapes of the spectra of various K x-ray lines has been investigated in detail for Pd, Tb, Ta and Th. It has been found that in the KL⁰M¹ satellite spectra the shapes of the bands mainly resemble the shapes of the corresponding K x-ray diagram lines (but they are wider than the latter). For each element, the biggest average energy shifts with respect to the diagram lines are observed for a given kind of the KL⁰M¹ lines mostly in the case of removing a 3p electron in the initial state, whereas the smallest shifts are caused by removing a 3d electron. Our study can enable the correct quantitative interpretation of the K x-ray spectra of different multiply ionized medium-Z and heavy atoms (induced in collisions with light or heavy ions) and can be instrumental in planning various new experiments involving the determination of the M- and L-shell ionization probability.

A method for measuring the transmittivity of optical samples by using squeezed vacuum radiation is illustrated. A squeezed vacuum field generated by a below-threshold optical parametric oscillator is propagated through a non-dispersive medium and detected by a homodyne apparatus. The variance of the detected quadrature is used for measuring the transmittivity. With this method the number of photons passing through the sample during the measurement interval is drastically reduced. The results of some tests are reported.

We investigate the behaviour of the geometric phase of a bipartite system with intersubsystem coupling via a quantum jump approach, where one of the subsystems is driven by a one- or two-mode quantized field which is also subjected to decoherence. The results show that the first correction due to the decohering field is only quadratic in decaying rate λ when the evolution of the system is adiabatic, and the lowest order correction is related to the first order in λ when the evolution of the system is non-adiabatic. Moreover, an interesting interpretation of this phenomenon is given.

We present results of a theoretical investigation of the partial and total photoionization cross sections between the ¹D and ¹S thresholds of atomic fluorine using the multiconfiguration Hartree–Fock method of bound and continuum wavefunctions. The 2p⁴(¹S)ns, md series observed by an experiment through their decay into the allowed 2p⁴(³P)kl and 2p⁴(¹D)kl ionization channels are carefully identified. The 2s2p⁶²S resonance is seen to interact strongly with the nearby 2p⁴(¹S)4s ²S resonance. The results of the partial cross sections are first compared with the experimental observations. The total cross sections are compared with the available experimental and theoretical data. The energy positions of the resonance series 2p⁴(¹S)ns, md as well as 2s2p⁶²S excitation are found to be in very good agreement with the experimental observations.

The process of mutual neutralization in slow H⁺₂+H⁻ collisions is considered within the multi-channel Landau–Zener model. The cross sections for electron capture from H⁻ to specific gerade (singlet and triplet) states of H₂ molecule are calculated in the CM energy range from 0.05 keV/u to 5 keV/u. The calculated total mutual neutralization cross section is in satisfactory agreement with the experimental data available in the CM energy range 20–2000 eV.

A fully relativistic restricted active space (RAS) configuration interaction (CI) approach is employed to compute the P, T-odd interaction constant W_d of the ground ²Σ state of BaF. The present calculation estimates W_d = −0.352 × 10²⁵ Hz/e-cm. We also report the dipole moment μ_e of the ground state of BaF which is in good agreement with experiment.

The B-spline R-matrix method is employed to investigate the low-energy elastic electron scattering by atomic oxygen. Flexible non-orthogonal sets of radial functions are used to construct the target description and to represent the scattering functions. A detailed investigation regarding the dependence of the predicted partial and total cross sections on the scattering model and the accuracy of the target description is presented. The predicted angle-integrated elastic cross sections are in good agreement with experiment, whereas significant discrepancies are found in the angle-differential elastic cross sections near the forward direction. The near-threshold results are found to strongly depend on the treatment of inner-core short-range correlation effects in the target description, as well as on a proper account of the target polarizability. A sharp increase in the elastic cross sections below 1 eV found in some earlier calculations is judged to be an artefact of an unbalanced description of correlation in the N-electron target structure and the (N + 1)-electron collision problems.

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We correct the proof of the Brundobler–Elser formula (BEF) provided in Volkov and Ostrovsky (2004 J. Phys. B: At. Mol. Opt. Phys.37 4069) and continued in the appendix of Volkov and Ostrovsky (2005 J. Phys. B: At. Mol. Opt. Phys.38 907). After showing that some changes of variables employed in these articles are used erroneously, we propose an alternative change of variables which solves the problem. In our proof, we reveal the connection between the BEF for a general N-level Landau–Zener system and the exactly solvable bow-tie model. The special importance of the diabatic levels with maximum/minimum slope is emphasized throughout.

After using a corrected change of variables, Dobrescu and Sinitsyn (2006 J. Phys. B: At. Mol. Opt. Phys.39 1253) subsequently circumvent the direct calculation of the perturbation theory expansion by comparing the problem to the bow-tie model that was solved exactly previously (Ostrovsky and Nakamura 1997 J. Phys. B: At. Mol. Opt. Phys.30 6939). We argue that the direct calculations are feasible and interesting: for instance, they are able to enlighten the specific structure of the survival probability in the bow-tie model, as illustrated by some examples.