Angular asymmetry of resonant Auger decay of photoexcited Ar ${2\mathrm{p}}_{1\mathrm{/}2,3\mathrm{/}2}^{\mathrm{-}1}$4s states has been studied by high-resolution experiment, utilizing the Auger resonant Raman effect. The fine structures in the electron spectra have been resolved and the Β parameters for individual resonant Auger transitions have been derived. A careful comparison has also been carried out with earlier experimental studies as well as with the results of multiconfiguration Dirac-Fock calculations.

The eikonal formula for the scattering amplitude is investigated for the most general local potential between two spin one-half particles, i.e., that which includes a tensor interaction. The analysis isolates the main contribution to high-energy scattering near the forward direction, constructs from it eikonal solution approximations, and indicates the way to obtain successive corrections. The method is also applied to include a spin-orbit potential contribution. Closed-form expressions that depend on the potential components are given for the Green's function and the scattering amplitude for these approximations.

We report a high-resolution study (0.0036 nm full width at half maximum) of electron-impact-induced emission spectra of CO at 30-, 75-, and 100-eV electron-impact energies. The spectral features were acquired in optically thin conditions. At the specified resolution, attainable with our 3-m vacuum ultraviolet spectrometer, we observe rotationally resolved emission bands of CO in the extreme ultraviolet, from the vibronic states B${\mathrm{}}^1$${\mathrm{\Sigma }}^{+}$(0), C${\mathrm{}}^1$${\mathrm{\Sigma }}^{+}$(0), and E${\mathrm{}}^1$Π(0), to the ground state X${\mathrm{}}^1$${\mathrm{\Sigma }}^{+}$(0). A simple model of these bands, based on the Hönl-London factors and the rotational constants, is constructed and is shown to be in good agreement with the observed spectra. The predissociation yield for the E${\mathrm{}}^1$Π electronic state has been determined, showing that the E state has the largest predissociation cross section of CO for all singlet-state Rydberg series members. The excitation function of the [E${\mathrm{}}^1$Π(0)→X${\mathrm{}}^1$${\mathrm{\Sigma }}^{+}$(0)] transition, in the 0–800-eV impact energy range, is measured, permitting determination of the oscillator strength by using a modified Born approximation analytical fit.

Differential cross sections for the elastic scattering of 22.1-keV photons by 30 elements in the atomic region 12⩽Z⩽92 have been measured at an angle of 117°. The measurements were performed under vacuum using Si(Li) detector and ${}_{}{}^{109}{}_{}{}^{}\mathrm{Cd}$ radioisotope as photon source. The intensity of incident photons, detector efficiency, and other geometrical factors was determined by measuring the K x-ray yields from targets of various elements with 30⩽Z⩽52 excited by photons from ${}_{}{}^{109}{}_{}{}^{}\mathrm{Cd}$ and ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ radioactive sources and from the knowledge of K x-ray fluorescence cross sections. The present measured elastic scattering cross sections have been compared with those obtained in the independent-particle approximation through calculations of modified-relativistic form factors (MF's), a combination of MF"s and angle-independent 'anomalous' scattering factors (ASF's), and the relativistic second-order S matrix. The MF values are found to be enormously larger than the measured ones in case of elements with K-shell or ${\mathrm{L}}_1$-subshell binding energy in the vicinity of 22.1-keV incident photon energy, and exhibit general agreement for other elements. The MF values in combination with ASF's and the S-matrix values are found to be on an average higher by 9% and 12%, respectively, than the measured values. These deviations increase up to 20% in case of elements with K-shell or ${\mathrm{L}}_1$-subshell binding energy just below the incident photon energy, and further decrease to ∼5% in case of elements with K-shell binding energy above the incident photon energy. The measured values for Al and Mg having electron binding energies far away from the incident photon energy show good agreement with different calculations.

Long-range interaction potentials between two and three sodium atoms, between a sodium atom and a perfectly conducting wall, and for a sodium atom between two perfectly conducting walls, are calculated with an electric-dipole oscillator strength distribution constructed from combinations of experimental and theoretical energy levels, oscillator strengths, and photoionization cross section data, constrained by accurate values of oscillator strength sum rules. The leading dispersion coefficients for Na-Na and Na-Na-Na and the Lennard-Jones coefficient for the Na-wall system are determined. For Na-Na and for the Na-wall systems, the retarded (Casimir) potentials are also calculated.

The electron-impact ionization cross section for hydrogen near threshold is calculated using both time-dependent wave-packet and time-dependent Green's-function methods. The time-dependent Green's-function method also allows the calculation of the elastic cross section. The need for absorbing potentials was removed by allowing our fast waves to leave our two-dimensional grid. Two different models are used for the Coulomb interaction between the electrons: a cusp model with v(${\mathrm{r}}_1$,${\mathrm{r}}_2$)=1/${\mathrm{r}}_{>}$ and a linear model with v(${\mathrm{r}}_1$,${\mathrm{r}}_2$)=1/(${\mathrm{r}}_1$+${\mathrm{r}}_2$), both with all angular momenta set to zero. Between 0.2 and 2.0 eV the cusp model cross section may exhibit an exponential suppression, while the linear model cross section follows a power-law behavior with an exponent of 1.1 with no noticeable oscillations. The results of the numerical experiments are compared with previous classical and quantal predictions extending back over 40 years to the pioneering work of Wannier.

An interesting analytical expression is obtained for the coordinate probability distribution of a wave packet transmitted through a potential barrier. In the large-time asymptotics the distribution is given in terms of the transmission amplitude and the phase-space quasidistribution of the initial (not necessarily pure) state. The distortion of a (broad) wave packet due to the barrier penetration is determined by two timelike parameters, given by the energy derivative of the complex transmission amplitude. The resulting change of the packet shape reveals a dependence on the detector position and incorporates a possible speed-up effect and a negative dispersion.

Positron annihilation on a wide variety of atoms and molecules is studied. Room-temperature positrons confined in a Penning trap are allowed to interact with molecules in the form of low-pressure gases so that the interaction is restricted to binary encounters between a positron and a molecule. Data are presented for the γ-ray spectra resulting from positrons annihilating in such interactions. The Doppler broadening of these spectra is a measure of the momentum distribution of the annihilating electron-positron pairs. Consequently, these spectra provide information about the electron and positron wave functions. Systematic studies of annihilation line shapes are discussed for noble gases, a variety of inorganic molecules, alkanes, alkenes, aromatics, and perfluorinated and partially fluorinated hydrocarbons. In the case of molecules, the measurements are used to determine the probability of positrons annihilating at specific locations in the molecule. For example, in the case of partially fluorinated hydrocarbons, we have been able to determine the relative probability of annihilation on the fluorine atoms and on the C-H bonds. Insights that these studies provide in understanding the interaction of low-energy positrons with atoms and molecules are discussed.

Properties of two-center Coulomb Sturmian basis sets are discussed. Analytic and numerical techniques to calculate these functions and coupling matrix elements are developed. A class of Sturmian functions is found that has no analytic continuation to negative energies and is not present in one-center potentials. Advantages of Sturmian sets over conventional eigenstate sets are emphasized.

Photoelectron angular distributions from Ca ${4\mathrm{s}5\mathrm{p}}^1$P, maximally oriented using circularly polarized pulsed laser excitation, have been measured by rotating the linear polarization axis of a counterpropagating ionizing laser pulse. The angular distributions were measured as a function of ionizing energy in the near-threshold region encompassing the ${3\mathrm{d}4\mathrm{d}}^3$D and ${}_{}{}^3{}_{}{}^{}\mathrm{S}$ autoionizing resonances as well as the newly identified ${}_{}{}^1{}_{}{}^{}\mathrm{P}$ resonance of the same configuration. Isotropic angular distributions in the vicinity of the new resonance is consistent with its total angular momentum J=1 assignment. Remote from the resonances, the ratio of the dipole matrix elements for photoelectron s- to d-wave production is independent of ionizing energy, while the relative phase difference between these partial waves varies significantly. An interference between partial waves gives rise to a previously unobserved asymmetry in the photoelectron angular distributions which is shown to occur within an independent-particle model.

We calculate the spectrum of the scattered light from quantum degenerate atomic gases obeying Bose-Einstein statistics. The atoms are assumed to occupy two ground states, which are optically coupled through a common excited state by two low-intensity off-resonant light beams. In the presence of a Bose condensate in both ground states, the atoms may exhibit light-induced oscillations between the two condensates analogous to the Josephson effect. The spectrum of the scattered light is calculated in the limit of a low oscillation frequency. In the spectrum we are able to observe qualitative features depending on the phase difference between the macroscopic wave functions of the two condensates. Thus, our optical scheme could possibly be used as an experimental realization of the spontaneous breakdown of the U(1) gauge symmetry in the Bose-Einstein condensation.

In this paper we present an atom laser scheme using a Raman transition for the output coupling of atoms. A beam of thermal atoms (bosons) in a metastable atomic state is pumped into a multimode atomic cavity. This cavity is coupled through spontaneous emission to another cavity for the atomic ground state. Above a certain threshold pumping rate a large number of atoms build up in the lowest energy state of the second cavity, while the higher energy states remain unpopulated. Atoms are then coupled to the outside of the cavity with a Raman transition. This changes the internal level of the atom and imparts a momentum kick, allowing the atoms to leave the system. We propose an implementation of our scheme using hollow optical-fiber atom waveguides.

We analyze the time evolution of solutions of nonlinear Schrödinger equations that describe a condensate composed of atoms with negative scattering lengths in a harmonic potential trap. It is theoretically demonstrated that if an initial condensate has negative energies due to negative scattering lengths, then the solutions diverge in a finite time that is determined by the condensate's energy, its initial phase, and the trap parameter.

We derive a description of the spatially inhomogeneous Bose-Einstein condensate, treating the system locally as a homogeneous Bose gas. This approach, similar to the Thomas-Fermi model for the inhomogeneous many-particle fermion system, is well suited to describe the atomic Bose-Einstein condensates that have recently been obtained experimentally through atomic trapping and cooling. In this paper, we confine our attention to the zero-temperature case, although the treatment can be generalized to finite temperatures, as we shall discuss elsewhere. Several features of this approach, which we shall call the Thomas-Fermi-Bogoliubov description, are very attractive. (i) It is simpler than the Hartree-Fock-Bogoliubov technique. We can obtain analytical results in the case of weakly interacting bosons for quantities such as the chemical potential, the local depletion, pairing, pressure, and density of states. (ii) The method provides an estimate for the error due to the inhomogeneity of the Bose-condensed system. This error is a local quantity so that the validity of the description for a given trap and a given number of trapped atoms can be tested as a function of position. We see, for example, that at the edge of the condensate the Thomas-Fermi-Bogoliubov theory always breaks down. (iii) The Thomas-Fermi-Bogoliubov description can be generalized to treat the statistical mechanics of the Bose gas at finite temperatures.

A self-consistent mean-field (Hartree-Fock) theory for bosons for temperature T>0 is used to compute the spatial distribution of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ atoms in a harmonic trap. In light of recent experimental observations at Rice University, the goal is to establish the extent to which Bose-Einstein condensation (BEC) is possible with ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ atoms, and to deduce the most effective signature of BEC from observations of the spatial profile. Our Hamiltonian, which includes the anisotropic external trap field and atom-atom interactions, is equivalent to that used previously for trapped atomic hydrogen. However, the attractive atom-atom interaction creates a localized well near the origin and precludes use of the usual local-density approximation. Eigenfunctions for the lowest orbitals are obtained by iteration. The total density is obtained from a sum with Bose population factors for these explicitly computed orbitals, together with analytic sums for unperturbed (ideal gas) orbitals for higher-lying states. For a small range of temperatures near ${\mathrm{T}}_{\mathrm{c}}$, it is found that the atomic cloud exhibits a spatially localized ``condensate peak'' composed primarily of atoms in the ground state. For lower T, such that more than 800–1200 atoms are in the ground state, the calculations become numerically unstable as found previously for T=0. Computational results for the collisional spin-flip ejection rate for T near ${\mathrm{T}}_{\mathrm{c}}$ and an estimate of the fluctuation in the number of atoms in the condensate are presented.

In this paper, we present a method for simulating the kinetic evolution of a dilute gas of atoms that are cooled below the critical temperature for Bose-Einstein condensation. Our method gives insight into the formulation of physical kinetics by illustrating directly the decomposition of the distribution function into an infinite sum of single-particle trajectories. This approach is valid for the entire range of phase-space densities, although we limit the discussion here to exclude the region where the condensate fraction is close to unity and the effect of the mean field is significant. We present explicit calculations of finite number effects on equilibrium, the dynamic build-up of the ground state, and simulations of evaporative cooling.

We derive, using the classical Hamilton-Jacobi theory, exact and general relativistic expressions for the ponderomotive scattering angles of an electron which is incident initially with an arbitrary velocity on the focal region of a laser pulse of arbitrary intensity, polarization, and pulse shape. The result is used to analyze the experimental data recently obtained by Meyerhofer et al. [J. Opt. Soc. Am. B 13, 113 (1996)] and to predict the ponderomotive scattering angles for very high incident energies as envisaged in laser-accelerator experiments.

We present an experimental and theoretical investigation characterizing the flux of laser-guided atoms through hollow-core optical fibers and show how it depends on laser detuning from resonance, laser intensity, and fiber curvature. The guiding employs dipole forces arising from the interaction of the atoms with the optical field. Laser light is focused into the hollow region of 40-μm-inner-diam capillary fiber and guided through the fiber by grazing incidence reflection from the glass walls. The lowest-order mode is azimuthally symmetric with maximum intensity on the fiber axis and nearly zero intensity at the walls. Rubidium atoms are attracted to the high-intensity region along the axis when the laser is detuned to the red of resonance and consequently guided through the fiber. Of particular interest is the evolution of the atom-flux versus laser-detuning profile of increasing intensity. At low intensities the dipole guiding potential is purely conservative and the flux profile is roughly dispersion shaped. At high intensity, viscous dipole forces heat the atoms and ``burn a hole'' in the flux-detuning curve. We find that transverse heating of the atoms and the exponential attenuation of optical mode intensity limit the distance atoms may be guided to about 20 cm in a 40-μm-diam fiber. Bending the fiber can reduce the effects of heating on atom flux.

We have solved the time-dependent Schrödinger equation to analyze the time evolution of a hydrogen atom, initially in its ground 1s state, interacting with a one- or two-color linearly polarized laser pulse which is tuned close to a two-photon resonance with the 2s metastable state. The two-photon transition therefore does not involve an intermediate resonance state. Using a suitable combination of two laser pulses of different frequencies, population can be transferred from the 1s state to the 2s state via the continuum. In both the single-color and the two-color cases, a maximum amount of 17% of population can be found in the 2s state at the end of the pulse. We compare and interpret our results in terms of the time-independent Floquet eigenvalues. The system can also be modeled by an ``essential states'' two-level atom with decay. Both the Floquet and the time-dependent solutions are compared with the model predictions. The model allows systematic optimization studies for population transfer under a wide range of laser pulse parameters.

The probe-wave absorption spectrum calculation is presented for the case when a two-level atom or ion in the resonant field of laser radiation is subjected to low-frequency external action in such a way that parametric resonance takes place and the fine structure appears on the probe-wave absorption coefficient plot.