Density-functional theory in the local-spin-density approximation has been applied to calculate the energy positions of low-lying resonance (autoionization) states of neutral atoms and positive ions. This method is very convenient for a quick, approximate prediction of excitation energies in collision experiments.

The Ne photoabsorption spectrum in the region of the K edge has been measured with unprecedented energy resolution. The results have been interpreted by using an ab initio method that predicts natural linewidths, as well as relative intensities and positions of the different $1\overrightarrow{s}\mathrm{np}$ $(3\mathrm{}<~n<~6)$ transitions. The remarkable agreement between theory and experiment improves the spectroscopic characterization of these inner-shell excited states in an energy region where only electron-energy-loss spectroscopies were considered to provide accurate and high-resolution data.

The contribution of hadronic vacuum polarization to the hyperfine splitting of the muonium ground state is evaluated with the account of modern experimental data on the cross section of $e^{+}{e}^{-}\to \mathrm{annihilation}$ into hadrons.

The dc-field-induced tunneling rates for Li ${1s}^{2}2s{}^{2}S,$ ${1s}^{2}2p{}^2{P}^o,$ and ${1s}^{2}3d{}^{2}D$ states were computed from our previously published nonperturbative, many-electron quantum-mechanical theory. The results are compared to those obtained using formulas derived from one-electron semiclassical models. For small values of the field strength, the results exhibit the same behavior. However, quantitative as well as qualitative differences are observed for strong fields.

Absolute differential and total cross sections for single electron capture were determined from ${\mathrm{Kr}}^{+}$ ions on Ar in the energy range 0.3–5.0 keV. Using reduced variables $[\tau =E\theta$ vs $\theta \sin \left(\theta \right)d\sigma /d\Omega =\rho ],$ we deduced, from the experimental differential cross sections, that the electron capture channel “opens” at a critical projectile-target separation between ${1.63a}_0$ and ${2.21a}_0$ in the present energy range and that at least two different processes are involved. The total cross section for single electron capture is compared with other available measurements. These results give a general shape of the curve for single electron capture cross sections for the ${\mathrm{Kr}}^{+}-\mathrm{A}\mathrm{r}$ system in a wide range of energy.

We report the measurement of the absolute photoionization cross section for the ${6P}_{3/2}$ state of cesium. Cross sections were determined by measuring the photoionization rate of cesium atoms confined in a magneto-optical trap. The photoionization rate was measured by monitoring the decay of trap fluorescence during exposure to ionizing laser radiation. The measurements were made in the wavelength range 457.9 to 501.7 nm using several lines from an Ar-ion laser. Our results are compared to other experimental measurements as well as to existing theories.

The second-order perturbation theory in the framework of the Kramers-Henneberger oscillating frame representation of the Hamiltonian [H. A. Kramers, Quantum Mechanics (North-Holland, Amsterdam, 1956); W. C. Henneberger, Phys. Rev. Lett. 21, 838 (1968)] is used to study the tunneling process in a periodically driven double-well potential. The eigenstates of the Floquet Hamiltonian are efficiently approximated when a field frequency is larger than a classical frequency of the time-averaged Hamiltonian. The conditions for coherent enhancement and suppression of tunneling are obtained when the standard perturbation theory fails. It is shown that the enhancement and suppression of tunneling is due to field-induced coupling between states of a one-period averaged effective potential.

In a previous publication [Phys. Rev. A 55, 552 (1997)] we considered the effect of laser phase fluctuations on three-photon–one-photon phase control of resonance-enhanced photoionization. Here we extend those studies by considering the role of laser intensity noise in addition to laser phase noise. While our results indicate that relative intensity fluctuations between the fundamental field and its third harmonic have a significant effect on control, the contrast between constructive and destructive interference is nonetheless two orders of magnitude, even under (reasonable) worst case situations. Consequently, neither laser intensity nor phase fluctuations appear to pose a serious impediment to the efficient phase control of atomic and molecular processes.

In this paper we investigate the interaction of a single ion in a trap with laser beams. Our approach, based on unitary transformating the Hamiltonian, allows its exact diagonalization without performing the Lamb-Dicke approximation. We obtain a transformed Jaynes-Cummings-type Hamiltonian, and we demonstrate the existence of super-revivals in that system.

Energies and spatial observables for the ${}^1{\Sigma }_g$ state of the hydrogen molecule in magnetic fields parallel to the proton-proton axis are calculated with a guided random-walk Feynman-Kac algorithm. We demonstrate that the accuracy of the results and simplicity of the method may provide it a viable alternative to large basis-set expansions for small molecules in applied fields.

The spontaneous emission of a pair of two identical and fixed two-level atoms, sharing initially a single excitation, is considered. It is shown that the solution which involves all the retardation times obtained by Milonni and Knight [Phys. Rev. A 10, 1096 (1974)] is also valid for interatomic distances less than half of a transition wavelength. The effects of the interatomic distance on the time evolution of the atomic state populations are examined.

The self-focusing of femtosecond optical pulses in dielectric solids is studied under the influence of the combined effects of diffraction, Kerr nonlinearity, normal group velocity dispersion, and self-induced multiphoton ionization. The numerical simulations show a significant pulse shortening with a compression factor of 5.5 and self-channeling of the beam when the critical power is exceeded.

A unified semiclassical time propagator is used to calculate the semiclassical time-correlation function in three Cartesian dimensions for a particle moving in an attractive Coulomb potential. It is demonstrated that under these conditions the singularity of the potential does not cause any difficulties and the Coulomb interaction can be treated as any other nonsingular potential. Moreover, by virtue of our three-dimensional calculation, we can explain the discrepancies between previous semiclassical and quantum results obtained for the one-dimensional radial Coulomb problem.

A real-time observation of an ultrafast intracluster harpooning reaction in an electronically excited metal atom-molecule complex is reported. Using the laser pump-probe technique the intracluster bimolecular reaction ${\mathrm{Ba}\mathrm{\cdots }\mathrm{FCH}}_3{\to \mathrm{B}\mathrm{a}\mathrm{F}+\mathrm{C}\mathrm{H}}_3$ has been investigated both in the real-time and frequency domains. The directly measured reaction time of 250 fs is in very good agreement with the decay time obtained by inverse Fourier transformation of the photodepletion spectrum of the parent ${\mathrm{Ba}\mathrm{\cdots }\mathrm{FCH}}_3$ cluster.

Partial photodetachment and photoionization cross sections corresponding to highly excited residual atoms or ions are shown analytically to mirror one another in the neighborhood of a resonance. More precisely, any two groupings of partial cross sections are shown here to have components whose variations with energy near a resonance are equal in magnitude and opposite in direction. This work extends an analysis of Starace [Phys. Rev. A 16, 231 (1977)] for the behavior of partial cross sections near a resonance to the case when the ${\rho }^2$ parameter of Fano and Cooper [Phys. Rev. 137, A1364 (1965)] tends to zero.

The number of electrons emitted per incoming projectile has been measured for ${\mathrm{Xe}}^{25+}{-\mathrm{C}}_{60}$ collisions at 475 keV using a coincidence ion-by-ion technique. Emission statistics have been successively determined for 1 to 15 electrons being stabilized onto the projectile. The electron emission multiplicity has been observed up to 45 in reactions where transient ${\mathrm{C}}_{60}^{60+}$ ions rapidly exploded into ${\mathrm{C}}^{+}$ and ${\mathrm{C}}^{2+}$ fragments. The ratio of the number of ejected vs stabilized electrons was found constant, showing that the ejected electrons were autoionized by the hollow xenon atoms produced.

We experimentally create and theoretically explain a different type of highly anisotropic atomic angular-momentum distribution with two preferential axes. Such a biaxial spatial orientation is created by optical pumping with elliptically polarized light, and measured by the observation of coherent population trapping in a weak external magnetic field. We probe the angular-momentum distribution by the Hanle configuration, and observe two dark resonances at nonzero magnetic fields—the expected signature of the biaxial spatial geometry. A direct method for preparing arbitrarily oriented atomic ensembles is discussed.

A nonsequential ionization model based on dynamic electron correlation is used to analyze the intensity dependence of the laser-induced single- and double-ionization yields for He at five different laser frequencies. Predictions of the present theoretical model and the recent experimental results are found to agree remarkably well over the entire intensity range. The presence of the ubiquitous “knee” structure at the optical wavelengths and its absence at the ultraviolet wavelength are also reproduced by the theory.

We describe a resonance technique to probe the coupling between two spin systems at low magnetic fields. With the use of a single rotating magnetic field we match the Rabi frequency of one spin to the Larmor frequency of a second, thereby affecting the $T_1$ of the second spin species. We have used this technique to demonstrate the contribution of coupling to surface protons to the relaxation of gaseous and liquid laser-polarized ${}^{129}\mathrm{Xe}.$

A scheme to trap atoms in a blue-detuned optical dipole trap, formed with a single laser beam and a holographic phase plate, is demonstrated. ${10}^5$ rubidium atoms are trapped for (1/e lifetime) ∼300 msec, at temperatures of ∼24 μK and a density of $\sim 7\times {10}^{11}{\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}\mathrm{s}/\mathrm{c}\mathrm{m}}^3,$ for a trapping beam detuning of 0.1–30 nm. The time for a trapped atom to scatter one photon off the trapping beam is measured and found to be linear in the trapping laser detuning. At a detuning of 0.5 nm from resonance this time was measured to be ∼100 msec, indicating that the atoms are exposed on average only to ∼1/700 of the maximal light intensity in the trap. The use of a single laser beam allows for simple dynamical changes of the potential and large adiabatic compressions, while keeping the atoms mainly in the dark.