Measurements are reported for projectile K-Auger-electron emission, observed at 90° to the incident beam direction, during interactions of 60-keV ${\mathrm{N}}^{6+}$ ions with a clean Cu(001) target at grazing incidence angles in the range 0.2°–20°. Spectral features in the projectile K-Auger-electron spectra consistent with above-surface K-Auger-electron emission were observed at perpendicular velocities below 1.37×${10}^{\mathrm{-}2}$ a.u. (incidence angle Ψ<1.9°). At incidence angles below 0.8° (${\mathit{v}}_{\mathrm{\perp }}$<5.8×${10}^{\mathrm{-}3}$ a.u.) the above-surface K Auger yields were observed to saturate, reaching a maximum value of about 12% of the total K-Auger-electron production. The present results are in good agreement with earlier measurements.

Measurements have been made of projectile K-Auger-electron emission during interactions of 60-keV ${\mathrm{N}}^{6+}$ ions grazingly incident on a Au(011) single crystal whose work function was modified by submonolayer deposits of Cs. K Auger spectra were obtained for incidence angles in the range 0.3°–5°, using clean, as well as cesiated, Au surfaces whose work function had been reduced by as much as 3.3 eV. For incidence angles smaller than 5°, an enhancement on the above-surface K Auger component, relative to that observed for ‘‘clean’’ Au, could be discerned with decreasing surface work function, which appears to saturate below 0.7° (corresponding to an inverse perpendicular velocity of about 200 a.u${.}^{\mathrm{-}1}$) at approximately 30–35 %. The experimental results are compared with modeling studies of the work-function dependence of above-surface neutralization and projectile K Auger emission, using a simulation based on the classical over-the-barrier model that was modified to treat the case of a ‘‘two-component’’ surface. The simulation results agree qualitatively with the experimental results up to ${\mathit{v}}_{\mathrm{\perp }}^{\mathrm{-}1}$=200. At higher inverse perpendicular velocities, the simulated enhancement continues to increase and exceeds the clean Au result by more than a factor of 2 at ${\mathit{v}}_{\mathrm{\perp }}^{\mathrm{-}1}$=1000. Speculations about possible reasons for this discrepancy will be presented.

We report the results of a theoretical investigation of the formal relationship between effective-Hamiltonian and effective-Liouvillian dynamics. It is shown that there are some difficulties associated with the application of effective Hamiltonian dynamics to the modeling of spectral and temporal properties of quantum systems. More specifically, we provide a rigorous proof that effective-Liouvillian dynamics is not reducible to effective-Hamiltonian dynamics without discarding dynamical information about the interruption of certain phase coherences between the relevant and irrelevant parts of a system and the transfer of those phase coherences into phase coherences and excitations in the irrelevant part. It is shown that the discarded dynamical information makes a significant contribution to the frequency-dependent nonradiative decay rate for a simple model system.

We have acquired spectra of high Rydberg states of molecular hydrogen in a static external field, in the energy region from below the energy at which field ionization becomes classically possible (${\mathit{E}}_{\mathit{c}}$) to well above this energy. Simultaneous spectra of ionization and dissociation were acquired, thereby allowing direct information on the excited-state decay dynamics to be obtained. We have found that states with energies below ${\mathit{E}}_{\mathit{c}}$ undergo field-induced predissociation, while states with energies well above ${\mathit{E}}_{\mathit{c}}$ decay predominantly by field ionization. Field ionization and dissociation compete effectively as decay channels for states with energies in a restricted region just above ${\mathit{E}}_{\mathit{c}}$. Comparison of our ionization spectra to the results of a single-channel quantum-defect theory Stark calculation shows quantitative agreement except near curve crossings, indicating that inclusion of different core rotational state channels will be required to properly account for coupling between the Stark states. Several states in the spectra undergo pronounced changes in their dynamical properties over a narrow range of field values, which we interpret as being due to interference cancellation of the ionization rates for these states.

A parametric hyperfine-structure (hfs) analysis of 24 excited even-parity levels of the 4${\mathit{f}}^7$5d6s6p configuration in Gd i was performed. The interpretation has been carried out based on a refined multiconfigurational fine-structure (fs) calculation taking altogether 177 assignments into account. The set of fs parameters as well as the leading eigenvector percentages of levels relevant for this paper are given. SL-limit effective-operator expressions are presented for the magnetic-dipole and electric-quadrupole hfs of arbitrary states built from four open electron shells. The following single-electron hfs parameters ${\mathit{a}}_{6\mathit{s}}^{10}$ and ${\mathit{b}}_{6\mathit{p}}^{02}$ were deduced for ${}_{}{}^{155}{}_{}{}^{}\mathrm{Gd}$, ${\mathit{a}}_{6\mathit{s}}^{10}$=-1270(22) MHz, ${\mathit{b}}_{6\mathit{p}}^{02}$=1507(26) MHz and for ${}_{}{}^{157}{}_{}{}^{}\mathrm{Gd}$, ${\mathit{a}}_{6\mathit{s}}^{10}$=-1668(28) MHz, ${\mathit{b}}_{6\mathit{p}}^{02}$=1603(29) MHz. For the odd-parity level 4${\mathit{f}}^7$5d6${\mathit{s}}^2$ ${}_{}{}^7{}_{}{}^{}$${\mathit{D}}_4$ the magnetic-dipole A and electric-quadrupole B hfs constants were found to be ${}_{}{}^{155}{}_{}{}^{}$A=-11.3(2.1) MHz, ${}_{}{}^{155}{}_{}{}^{}$B=54(9) MHz, ${}_{}{}^{157}{}_{}{}^{}$A=-14.8(2.7) MHz, and ${}_{}{}^{157}{}_{}{}^{}$B=58(10) MHz. The validity of all single-electron hfs parameters was checked using general trends of the corresponding 〈${\mathit{r}}^{\mathrm{-}3}$${\mathrm{〉}}_{\mathit{n}\mathit{l}\mathit{s}}^{\mathit{k}}$${\mathit{k}}_{\mathit{l}}$ values known for the series of the lanthanides. Finally, the evaluation of the electric nuclear quadrupole moment is discussed.

A class of approximate solutions of the Schrödinger equation for an atom in a time-dependent electric field that scales with the applied field F as FF(t)dt is derived and their bounds of validity are carefully examined. The class covers a wide region of applicable electric fields and its time constants. An extensive comparison of these solutions with the results of numerical calculations on a truncated basis of up to 465 hydrogenic states shows surprising agreement. One of these solutions is found to be very effective in field dressing of high Rydberg states. The resulting field dressing is proposed for the description of the plasma field effects on atomic reaction rates, but its range of applicability can be extended to the other atomic problems that involve time-dependent electric fields.

We give a solution of the three-dimensional Schrödinger equation for the electron of a hydrogen atom in external electric and magnetic fields of arbitrary mutual orientation. The rearrangement of the energy spectrum due to changing in the mutual orientation of the fields is evaluated by using the n=2 multiplet as an example. The calculations agree with second-order perturbation formulas that exist for the special cases of mutually parallel and orthogonal fields. For another special two-dimensional case which is currently being extensively investigated, namely, the hydrogen atom in a strong magnetic field, our approach agrees with calculations by other authors and yields more accurate binding energies for certain low-lying excited states that have been considered.

The calculation of the S matrix for a system acted upon by an external electromagnetic field, when the fully interacting system can be represented by normalized Floquet states, is reformulated to include adiabatic switching and wave-function renormalization. This procedure yields, in general, nonvanishing matrix elements between states whose energies differ by an integral multiple of the photon energy. The induced level shifts do not disturb this condition; however, a relative level shift between the initial (in) and final (out) states is essential for a transition to occur. A numerical scheme to facilitate use of this formalism in practice has been devised and applied to a model calculation. The present nonperturbative results agree with lowest-order perturbation theory for weak fields, but deviate towards lower values at higher field strengths. Representative data for the simultaneous excitation of more than one level are presented to show that transition amplitudes are well defined in the presence of intermediate resonances. Gauge dependence of the level shifts and transition amplitudes is also studied, both theoretically and numerically.

It is shown how the concept of the ponderomotive potential of a free point charge is to be generalized for atoms and molecules, and its connection with the dynamic Stark shift is clarified. For the harmonic oscillator both are calculated in a nonperturbative way. The so-called ponderomotive term in the atomic Hamiltonian, which is quadratic in the vector potential A, corresponds to no physical reality.

We report a Rydberg-atom experiment, demonstrating the dynamic suppression of spontaneous emission in a resonant microwave cavity driven by a resonant external field. If the Rabi frequency of the injected field is larger than the atomic and cavity line widths, the atoms almost completely decouple from the cavity mode due to suppressed field fluctuations at the sideband frequencies of the Mollow triplet. This was achieved with about 100 microwave photons in the cavity. The reduced decay rate is a consequence of non-Markovian dynamics induced by the finite cavity-response time.

We examine theoretically the recent experiments of Lange and Walther on the dynamical interaction of Rydberg atoms in a microwave cavity in the presence of a strong driving field. In particular, we study how the intense field renormalizes the cavity-induced spontaneous emission. For this purpose we derive the master equation for the atomic dynamics by adiabatically eliminating the cavity-field variables, while treating the intense driving field nonperturbatively. We present analytical and numerical solutions of the master equation, taking into account the turn on and turn off of the atom-field coupling in the rest frame of the atoms, as well as the velocity distribution of the atomic beam. We obtain good agreement between theoretical results and experiments.

The interaction between a parametric oscillator and a stream of polarized two-level atoms is considered. The dynamics of the system is computer simulated and the atom-field evolutions are followed. Different steady states are obtained with enhanced squeezing and sub-Poissonian statistics, depending on the atomic and parametric oscillator pump phases. The results are interpreted in terms of damping by a rigged reservoir.

We have investigated the high-order harmonic generation of a subpicosecond KrF laser (248 nm) using nine ionic species in laser-produced plasmas. The highest order of the 21st harmonic (11.8 nm) has been observed in a lead plasma. The maximum observed harmonic orders in various ions and neutral rare gases are found to be proportional to the ionization potentials of these species. We have obtained superior results for the high-order harmonic generation by using ions compared to using neutral rare gases, and have demonstrated the advantages of using ions as nonlinear media to generate extreme ultraviolet radiation.

Optical pumping of atomic vapors can lead to self-focusing of resonant laser beams. The saturation of the optical pumping process at low intensity allows the study of transverse solitons in the form of self-trapped laser beams, using low-power cw lasers. The long lifetime of the optically pumped atoms allows the atomic diffusion to transport the excitation away from the interaction region. Numerical simulations show that the resulting nonlocal response of the medium represents an important mechanism that stabilizes the self-trapped beam. The theoretical predictions are confirmed by experimental results from sodium vapor.

The effects of laser parameters such as intensity, wavelength, and bandwidth on the determination of the Sn isotope ratio are analyzed numerically with density-matrix equations. The bandwidth of the laser is taken into account by the chaotic-field model. We consider the isotopes of Sn that consist of the even-mass isotopes with no nuclear spin and the odd-mass isotopes with a nuclear spin of ħ/2. In the scheme in which a first laser excites atoms to an intermediate state and a second laser ionizes them, the exciting-laser intensity has greater influence on the isotope ratio than the ionizing-laser intensity regardless of the laser bandwidth. As regards the laser bandwidth, a comparison is made between the broad bandwidth that overlaps all intermediate levels of the isotopes and the narrow bandwidth that is small enough to excite only the intermediate level of the even-mass isotopes. The even-mass isotopes whose intermediate level is on resonance are more ionized than the odd-mass isotopes when the intensity of the broadband exciting laser is small, while the odd-mass isotopes are more ionized when the intensity of the narrow-band exciting laser is large. The isotope ratio is sensitive to the exciting-laser wavelength even when the laser bandwidth is broad.

Simple analytical expressions for the time evolution of the mean photon number and its normally ordered variance for the case of an initially thermal cavity field coupled to an initially unexcited two-level atom are proposed. The possibility of appearance of sub-Poissonian field statistics is discussed.

The deteriorating effect of low-efficiency detectors in different schemes suitable for a direct measurement of the Q function and in optical homodyne tomography is studied in some detail. It turns out that this effect amounts to smoothing the respective quasiprobability distribution that would be measured with unit-efficiency detectors. Our main result is that those smoothed distributions can be identified with certain s-parametrized quasiprobability distributions. Thus the latter gain direct experimental significance as distributions measurable under realistic experimental conditions.

We study the Swift-Hohenberg equation describing a passive optical cavity driven by an external coherent field, valid close to the onset of optical bistability. A linear analysis shows that the system can sustain nontrivial stationary structures for small positive detunings. A weakly nonlinear analysis in the vicinity of the instability points reveals the existence of stable hexagonal structures which eventually give way to rolls. Numerical simulations support such a bifurcation scenario.

Two-photon interferometry can produce violations of Bell’s inequality that demonstrate the nonlocal nature of such effects. It is shown here that high-intensity fields containing large numbers of photons can violate Bell’s inequality in a similar manner. The macroscopic nature of these fields is evident from the fact that they can produce large bursts of energy in two distant absorbers with nonlocal correlations between the two.

We present a quantum analysis of the measurement of a relative optical phase using a many-port method that can be implemented using arrays of photodetectors in the limit of a large number of detector elements. Its application to coherent states and states not describable by the semiclassical theory shows that the many-port method has in principle several advantages compared to an eight-port method previously studied. In some cases, especially for very weak fields, the many-port method provides a more faithful characterization (i.e., a smoother distribution) of the distribution of the relative phase than does the eight-port method. The definition used here for the relative phase between two fields is an operational one, not corresponding to any presently known Hermitian phase operator. We discuss the conditions under which our phase definition corresponds to the best estimate in the maximum-likelihood sense. We find that if the many-port data set is analyzed in a way that retains the contributions from zero photon counts, the many-port phase distribution takes on a character that resembles other phase distributions, such as the Pegg-Barnett or Wigner phase distributions, that show very small modulation depth in the case of weak fields.