Collisions between ground-state helium atoms and excited barium atoms in the ${\mathrm{}\left(6p\right)\mathrm{}}^3{P}_J,$ ${\mathrm{}\left(5d\right)\mathrm{}}^1{D}_2,$ and ${\mathrm{}\left(5d\right)\mathrm{}}^3{D}_J$ states are treated theoretically. Born-Oppenheimer potential curves are calculated with a combination of semiempirical model potentials and pseudopotentials to represent the interactions between the valence electrons of the barium atom and the closed-shell cores. The molecular basis set is constructed from numerical eigenstates of the ${\mathrm{Ba}}^{+}$ ion. Spin-orbit coupling is included explicitly in the $e^{-}-{\mathrm{Ba}}^{2+}$ interaction Hamiltonian. We report higher-lying potential curves correlated with the metastable ${(5d}^2{)}^3{F}_J$ states.

We develop a theoretical description of collisions between an excited barium atom in the $6s6p{}^3{P}_J,$ $6s5d{}^1{D}_2,$ or $6s5d{}^3{D}_J$ state and a helium atom in the ground state. Using the adiabatic potential curves presented in the preceding paper, state-to-state cross sections are obtained from a fully quantum-mechanical close-coupling calculation using the generalized log-derivative approach. Our theoretical results are compared to recent experimental data.

Total-electron detachment cross sections for ${\mathrm{H}}^{-}$ colliding with multiply charged ${\mathrm{Ne}}^{4+}$ and ${\mathrm{Ar}}^{4+}$ ions are calculated using the two-center atomic-orbital close-coupling expansion method in the center-of-mass energy range of 4–200 keV. The calculation shows that there is no core effect, and that electron capture only plays a minor role for energies above 20 keV. At 50 keV, where electron capture is not important, the single-center atomic-orbital expansion method was used to calculate the detachment cross sections for incident charges $q=1\mathrm{}$–8. The present calculations are shown to be in good agreement with experimental data.

Laser excitation of In atoms at the $6{}^2{S}_{1/2}–5{}^2{P}_{1/2}$ atomic resonance transition wavelength of 410.3 nm in the presence of Hg vapor produces several types of emission features: HgIn excimer satellites on the red wings of the In resonance fluorescence transitions at 410.3 and 451.1 nm, bound-bound HgIn molecular fluorescence at 499 and 522 nm resulting from photoassociation of $\mathrm{In}\left(6\mathrm{}{}^2{S}_{1/2}\right)$ with $\mathrm{Hg}\left(6\mathrm{}{}^1{S}_0\right),$ and UV atomic fluorescence from the $\mathrm{In}\left(5\mathrm{}{}^{2}D\right)$ states that lie at energies above the $\mathrm{In}(6\mathrm{}{}^2{S}_{1/2}–5{}^2{P}_{1/2})$ excitation. These various spectral features are interpreted in terms of a proposed HgIn potential-energy level diagram with additional information from measured excited-state lifetimes and the power dependence of the laser excitation at 410.3 and 522 nm. Direct excitation of the 499 and 522 nm HgIn bound-bound transitions also produces emission at 410.3 and 451.1 nm resulting from collisional dissociation of the excited HgIn states.

The role of surface plasmon excitation in the interaction of ions passing through thin films has been studied in both the Bloch hydrodynamic approximation and the local response approach for projectile velocities above the maximum of the stopping power curve. The effect of the surface is found to be much weaker when the dispersion of the modes is taken into consideration than in the case of nondispersive media, though qualitatively the main features of the hydrodynamic approach resemble those of the local one. A generalization of the Bothe-Landau convolution formula for the loss probability distribution is derived to take into account the scattering due to the surface. The effects of the surface in the energy-loss spectra are discussed. A comparison with experiment is given.

We investigate the possibilities of distinguishing the mean-field and fluctuation effects on the critical temperature of a trapped Bose gas with repulsive interatomic interactions. Since in a direct measurement of the critical temperature as a function of the number of trapped atoms these effects are small compared to the ideal gas results, we propose to observe Bose-Einstein condensation by adiabatically ramping down the trapping frequency. Moreover, analyzing this adiabatic cooling scheme, we show that fluctuation effects can lead to the formation of a Bose-Einstein condensate at frequencies which are much larger than those predicted by the mean-field theory.

We show that the phase difference of two overlapping ground-state Bose-Einstein condensates can affect the optical spontaneous emission rate of excited atoms. Depending on the phase difference the atom-stimulated spontaneous emission rate can vary between zero and the rate corresponding to all the ground-state atoms in a single condensate. Besides giving control over spontaneous emission this provides an optical method for detecting the condensate phase difference. It differs from previous methods in that no light fields are applied. Instead the light is spontaneously emitted when excited atoms make a transition into either condensate.

The deleterious effects of dispersion on a propagating coherent atomic pulse, along the axis of a traveling-wave laser beam, can be ameliorated by the nonlinear self-interacting force due to dipole-dipole coupling between atoms. We show that a wide atomic pulse with a particular profile can retain its shape during propagation and, moreover, the momentum of the pulse increases due to photon absorption. For the wide soliton case, we demonstrate analytically that the self-interacting atomic force scales inversely with the third power of the pulse width.

We study the quantum field theory of light-matter interactions for quantum degenerate atomic gases at low light intensity. We argue that the contact interactions between atoms emerging in the dipole gauge may be ignored. Specifically, they are canceled by concurrent infinite level shifts of the atoms. Our development yields the classic Lorentz-Lorenz local-field shift of the atomic resonance.

The mean field for atoms undergoing ground-state collisions in a gravito-optical trap is determined in a fully self-consistent way. The atoms are confined by gravity and one atomic mirror formed by an evanescent laser wave. The vertical density distribution of the trapped Bose gas at zero temperature and the refractive modification of the electromagnetic field are obtained iteratively. In the regime of nearly total internal reflection, the sensitive variation of the evanescent wave with the index of the gas leads to large dipole-dipole shifts. In the limit of a steep evanescent wave and large detuning, ground-state interactions dominate.

An atom laser is an as-yet unrealized device that would produce an atomic field analogous to the electromagnetic field of a photon laser. Here I argue that for this analogy to be meaningful it is necessary to have a precise definition of a laser that applies equally to photon or atom (or any other boson) lasers. The definition I propose uses the fundamental principle that the output of a laser is well approximated by a classical wave of fixed intensity and phase. This principle yields four quantitative conditions that the output of a device must satisfy in order for the device to be considered a laser. While explaining these requirements, I analyze the similarities and differences between atom and photon lasers. I next show how these conditions are satisfied first by an idealized photon laser model, and then by a more general model that can apply to atom lasers also. Lastly, I briefly discuss the current proposals for atom lasers and whether they could be true lasers.

We present an atom interferometer based on the interference of three partial matter waves in three different internal and external states. Coherent laser excitation acts as a beamsplitter to create a superposition state of the ground state and two Zeeman sublevels of the metastable state of magnesium atoms. The interference pattern of the output ports shows high contrast and the characteristics of three-beam interferences as known from optical interferometry. In comparison to two-beam interferometry a reduction of the fringe width of (32±8)% is observed. This offers various possibilities for improved measurements of quantum-mechanical phases due to the internal atomic-state sensitive coupling of external potentials. This is demonstrated for the interaction of magnesium atoms with an external magnetic field.

A treatment of the spin-rotation coupling between alkali-metal atoms and He atoms is presented. Rotational distortions are accounted for in the wave function using a Coriolis interaction in the rotating frame. The expectation value of the spin-orbit interaction gives values of the spin-rotation coupling that explain previous experimental results. For spin-exchange optical pumping, the results suggest that lighter alkali-metal atoms would be preferred spin-exchange partners, other factors being equal.

Experimental spectra for excited-state optical collisions between $\mathrm{Mg}\left(3p{}^1{P}_1\right)$ atoms and rare-gas atoms are presented. Aligned Mg atoms are produced in the $3p{}^1{P}_1$ level by excitation with linearly polarized light. Collisions between the excited metal atoms and Ne or Ar rare-gas atoms are probed in a $1000-{\mathrm{cm}}^{\mathrm{-}1}$ range in the vicinity of the Mg $3p{}^1{P}_1\to 5s{}^1{S}_0$ and $3p{}^1{P}_1\to 4d{}^1{D}_2$ transitions. The probe radiation is linearly polarized either along or perpendicular to the alignment axis, leading to a linear polarization for the optical collision process as a function of detuning of the probe from the atomic resonances. Substantial spectral variation of the linear polarization reflects the different molecular transitions responsible for the excitation process, and the evolution of the atomic alignment into the molecular regime. In the present case, the transitions correspond to excitation from the Mg–rare-gas $3p{}^1{\Pi }_1$ and $3p{}^1{\Sigma }_0^{+}$ molecular terms to the $5s{}^1{\Sigma }_0^{+},$ $4d{}^1{\Delta }_2,$ $4d{}^1{\Pi }_1,$ and $4d{}^1{\Sigma }_0^{+}$ terms. Experimental details of the approach, and the results obtained, will be described. Discussion of the polarization spectra is made through theoretical modeling focusing on the effects of the symmetry of the molecular states involved in the process. The modeling employs the semiclassical theory developed earlier. For a range of qualitatively correct interaction potentials and corresponding Condon points for the photo-excitation channels, good agreement between experiment and theoretical estimates is obtained.

We carry out quantum and semiclassical numerical simulations of the dynamics, particularly diffusion, of atoms in an optical lattice. We consider specifically the situation of a $J=1/2\mathrm{}\leftrightarrow J=3/2\mathrm{}$ atomic transition, whose experimental counterpart can be realized in ${\mathrm{Mg}}^{+}$ experiments. The semiclassical results, which cover a larger range of parameters than would be practical for fully quantum calculations, confirm and extend the work of Marksteiner et al. [Phys. Rev. A 53, 3409 (1996)], characterize the transition from normal to anomalous diffusion and the atomic trajectories which give rise to it, and provide a physical explanation for the difference between these two regimes. The full quantum calculations reveal uniquely quantum features of individual atomic trajectories, and in addition, predict significantly lower diffusion, by a factor of 1.2 to 2, than their semiclassical counterparts.

We give a systematic analysis of the extension of the one-dimensional velocity-selective coherent population trapping cooling mechanism to atoms with integer angular momenta $F>\mathrm{}1\mathrm{}$ using additional light shifts to compensate for the kinetic energy mismatch between the various Zeeman sublevels contributing to the internally decoupled (i.e., dark) state of the atom. Different configurations to achieve the proper light shifts to obtain a very long lifetime of the velocity-selective dark states are discussed and compared. In addition we show that the maximum occupation probability of the resulting quasidark state and its filling time scale strongly depend on the proper choice of detunings to exploit extra precooling mechanisms involving the Zeeman sublevels not contributing to the dark state. We show that additional cooling can also be implemented on the hyperfine repumping transition. This result should prove important for other schemes involving gray states such as, e.g., dark optical lattices and superlattices as well. As a concrete example we consider cesium including all relevant hyperfine levels.

In order to provide a model for more complex systems, we investigate coherent control of the quantum-mechanical transmission probability of wave packets approaching two rectangular barriers that form a finite potential well. We introduce an index to quantify the degree of achievable control. Factors that influence the control include properties of the potential, the number of incident packets, their spacing, and their energy profiles. For a chain of two resonant Gaussian packets, we isolate the effect of the decay lifetime of the resonance to which the incident packets are tuned. The effects of the packet energy widths and the packet spacing are considered for the same system. The investigation then expands to include longer Gaussian chains. A separate inquiry focuses on the effect of the energy profile of a single resonant waveform on the transmission probability. Throughout, we apply the variational formulation developed by Wilson and co-workers [J. Chem. Phys. 99, 6562 (1993)] and by Dubov and Rabitz [Phys. Rev. A 54, 710 (1996)].

The dynamics of multielectron dissociative ionization (MEDI) of ${\mathrm{H}}_2$ in an intense IR laser pulse are investigated using a wave-packet propagation scheme. The electron tunneling processes corresponding to the successive ionizations of ${\mathrm{H}}_2$ are expressed in terms of field-free Born-Oppenheimer (BO) potential energy surfaces (PES) by transforming the tunnel shape resonance picture into a Feshbach resonance problem. This transformation is achieved by defining a new, time-dependent electronic basis in which the bound electrons are still described by field-free BO electronic states while the ionized ones are described by Airy functions. In the adiabatic, quasistatic approximation, these functions describe free electrons under the influence of the instantaneous electric field of the laser and such an ionized electron can have a negative total energy. As a consequence, when dressed by the continuous ejected electron energy, the BO PES of an ionic channel can be brought into resonance with states of the parent species. This construction gives a picture in which wave packets are to be propagated on a continuum of coupled electronic manifolds. A reduction of the wave-packet propagation scheme to an effective five-channel problem has been obtained for the description of the first dissociative ionization process in ${\mathrm{H}}_2$ by using Fano’s formalism [U. Fano, Phys. Rev. 124, 1866 (1961)] to analytically diagonalize the infinite, continuous interaction potential matrix and by using the properties of Fano’s solutions. With this algorithm, the effect that continuous ionization of ${\mathrm{H}}_2$ has on the dissociation dynamics of the ${\mathrm{H}}_2^{+}$ ion has been investigated. In comparison with results that would be obtained if the first ionization of ${\mathrm{H}}_2$ was impulsive, the wave-packet dynamics of the ${\mathrm{H}}_2^{+}$ ion prepared continuously by tunnel ionization are markedly nonadiabatic. The continuous ionization appears to give rise to a population in the dissociative continuum that is localized at small internuclear distances throughout the action of the laser pulse, and is released only when the laser pulse is over, yielding a complex fragment kinetic energy spectrum. Comparison with available experimental data is made.

We report experimental investigations on dissociation of H${}_2$ and D${}_2$ in intense subpicosecond laser pulses at 1053 and 526.5 nm. Intensities in the range from $\approx 5\times {10}^{13}$ up to $\approx 5\times {10}^{14}$ W/cm${}^2$ were applied. The kinetic-energy distributions of the photoions H${}^{+}$ and D${}^{+}$, which change dramatically with the light pulse peak intensity, give a detailed insight into the dissociation mechanisms. At 526.5 nm and low light intensity, ions from bond-softening dissociation and probably seven-photon resonant dissociative multiphoton ionization dominate the spectra. The resonant intermediate states are Rydberg states of the neutral molecules. At 1053 nm, above-threshold dissociation makes the main contribution to the spectra. Independent of the excitation wavelength, Coulomb explosion dissociation is found in the high-intensity limit. ${\mathrm{H}}_2^{+}$ and ${\mathrm{D}}_2^{+}$ photoionization, triggering this process, proceeds in the quasistatic limit by preferred tunnel or above-barrier ionization in a limited range of internuclear separations around $7.5$ a.u. The ion kinetic-energy distributions seem to indicate that at 526.5 nm ionization starts from molecular ions light stabilized in a certain range of internuclear distances. In contrast, at 1053 nm, ionization seems to start from dissociating molecular ions.

We present a theoretical description of the appearance of bound states of atomic multiply charged negative ions of hydrogen in circularly polarized laser fields, using high-frequency Floquet theory (HFFT). Monochromatic circularly polarized fields with frequencies large compared to the binding energy of the dressed ion can (founded by HFFT) induce doubly and triply charged negative ions of hydrogen. The field conditions required to induce these ions are within experimental reach. A circularly polarized field with a wavelength $\lambda =456\mathrm{}\mathrm{nm}$ and an intensity $I=3.0\mathrm{}\times {10}^{17}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ can induce the appearance of a bound state of ${\mathrm{H}}^{2\mathrm{-}},$ whereas a bound state of ${\mathrm{H}}^{3\mathrm{-}}$ can be induced by a field with wavelength $\lambda =45.6\mathrm{}\mu \mathrm{m}$ and intensity $I=5.1\mathrm{}\times {10}^{13}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2.$ We also show that a relativistic description or a low-frequency theory is required in order to determine the appearance of bound states of more highly charged negative ions.