We present a theoretical description of the multiple ionization of atoms by a poweful circularly polarized laser field. Our calculations are based on the statistical model of the atom. The modified Thomas-Fermi equation in the rotating frame has been derived. Appearance intensities versus laser frequency have been plotted and discussed. The instability of the solution for circularly polarized laser light of sufficiently high frequency is expected.

We have observed a sudden reversal in the direction of population transfer between nearly degenerate Zeeman sublevels during optical pumping of the cesium 6${\mathit{S}}_{1/2}$(F=4)→6${\mathit{P}}_{3/2}$(F’=5) cycling transition. As a result of the reversal, the number of atoms in an atomic beam, with quantum numbers 6${\mathit{S}}_{1/2}$ (F=4; ${\mathrm{m}}_{\mathit{F}}$=-4), is a function of laser frequency and has a sharp dispersive shape. A rate-equation model indicates that similar dispersive shapes for the population can be expected in the optical pumping of any nondegenerate system with more than two levels, if the level spacing is much smaller than the laser linewidth.

We calculate the positive-energy spectrum of both hydrogen and lithium atoms in a field of 6.1 T and we show how such spectra can be obtained for an atom or molecule in an arbitrary strength magnetic field. The theory combines quantum-defect theory, R-matrix propagation, and two-dimensional frame transformations. Much of the resonance structure in the continuum can be understood in terms of complex perturbed Rydberg series.

When resonant collisional energy transfer occurs in a radiation field of frequency comparable to the inverse of the collision time, Ramsey interference fringes are observed in the cross section. At low frequencies the fringes are phase dependent, but at high frequencies they are not. The fringes may be understood with a quasistatic field description, which ties together the low- and high-frequency regimes.

Electron energy spectra have been measured that result from K-shell ionization of Kr by two different mechanisms: (1) photoionization and (2) internal conversion in the decay of the isomeric state of ${}_{}{}^{83}{}_{}{}^{}\mathrm{Kr}$. It is demonstrated experimentally that these spectra, including satellites on the low-energy side of the primary 1s-electron peak, are identical. A theoretical interpretation of the identity of the spectra is given. The spectra agree well with a relativistic many-electron calculation in which the satellites are attributed to excitation and ionization of M and N electrons during the K-ionization process.

Using the multifractal approach, we derive the probability distribution function (PDF) of the velocity gradients in fully developed turbulence. The PDF is given by a nontrivial superposition of stretched exponentials, corresponding to the various singularity exponents. The form of the distribution is explicitly dependent on the Reynolds number. The experimental data are in good agreement with the PDF predicted by the same random beta model used to fit the scaling of the velocity structure functions.

Brillouin scattering shows that at GHz frequencies the bending rigidity of surfactant layers in a swollen lyotropic lamellar liquid crystal is ≃${10}^3$ times larger than that found at low frequencies via x-ray, light-scattering, and static-force measurements on the same system.

We present results of path-integral Monte Carlo simulations of bosons on a two-dimensional square lattice in a random potential of average strength V and with on-site repulsion U. We find that the superfluid density ${\mathrm{\rho }}_{\mathit{s}}$ is enhanced by increasing V and U in certain regions of parameter space. By combining the results of ${\mathrm{\rho }}_{\mathit{s}}$, with the behavior of the density-density correlation function on lattices of size up to 10×10, we study the superfluid–to–Mott-insulator transition and the transition from a superfluid to a disorder-localized (‘‘Bose glass’’) phase.

The monopole (L=0) and quadrupole (L=2) strength distributions in normal ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ clusters are calculated within the random-phase approximation. We use a phenomenological, zero-range ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^3{}_{}{}^{}$He interaction to generate the Hartree-Fock single-particle spectrum and the residual particle-hole interaction. The evolution of the collective modes with the number of atoms in the cluster is discussed.

It is argued that the standard model of weakly interacting two-level systems (TLS) is compatible with the proposal that low-temperature properties of glasses are determined by strongly interacting defects. Typical strongly interacting defects have their tunneling suppressed, and observable tunneling occurs only for TLS which appear to be weakly coupled because their interactions are frustrated. Localized TLS are generated rather than collective modes because tunneling lowers the energy of the system. This explains both the success and the universality of the TLS model.

Electron holography using the Möllenstedt-type electron biprism [G. Möllenstedt and H. Düker, Z. Phys. 145, 377 (1956)] is now able to improve resolution and expressiveness of the electron microscope by subsequent correction of its aberrations and unique determination of amplitude and phase, as suggested by Gabor.

The ${\mathit{v}}_{1\to 2}$ hot band of the Si-H stretching vibration of the H/Si(111) 1×1 surface is investigated using picosecond sum-frequency generation. The hot band is probed after directly exciting the fundamental ${\mathit{v}}_{0\to 1}$ and found to be 90 ${\mathrm{cm}}^{\mathrm{-}1}$ lower than the fundamental. The shift is consistent with the Si-H anharmonicity in the gap phase and a small dispersion (11 ${\mathrm{cm}}^{\mathrm{-}1}$) for the surface layer, implying a strong two-phonon bound state.

We report a temperature-dependent study of the vibrations and the structure of Cu(110) using molecular-dynamics codes based on potentials obtained from the embedded-atom method. The calculated linewidths and frequencies of the surface phonons and resonances and the mean-square vibrational amplitudes of the atoms indicate a sharp rise in surface anharmonicity at about 600 K. Additionally, vacancies and adatoms begin to appear in the simulations of Cu(110) around 900 K. Comparison is made with experimental data and simulations of Cu(100).

We calculated the relative stabilities of carbon clusters with up to 60 atoms. Equilibrium geometries have been obtained by combining an adaptive simulated annealing method and a simple tight-binding-type Hamiltonian for total energies. We found that ${\mathrm{C}}_{\mathit{n}}$ clusters favor one-dimensional structures for n≲20. For n≳20, closed fullerene cages show a larger stability than both the one-dimensional and two-dimensional structures (such as graphite flakes and buckled fullerene ‘‘caps’’). Isomers with linear and ‘‘fullerene’’ structure should coexist near the critical cluster size n≊20. We find the ${\mathrm{C}}_{60}$ fullerene to be the most stable structure, with a binding energy of 6.99 eV/atom.

The optical deformation-potential constant, otherwise inaccessible in undoped materials, is measured in CdSe by optical spectroscopy with subpicosecond time resolution. The phonon-assisted transitions from B to A excitons occur with a decay time of 0.9 ps, determined by pump-and-probe experiments. An analytic expression for the transition time is obtained. Since the Fröhlich interaction is symmetry forbidden, we use a nonpolar optical Hamiltonian and extract a deformation-potential constant of ${\mathit{d}}_0$=32 eV.

We calculate absolute formation energies of native defects in GaAs. The formation energy and hence the equilibrium concentration of the defects depends strongly on the atomic chemical potentials of As and Ga as well as the electron chemical potential. For example, the Ga vacancy concentration changes by more than ten orders of magnitude as the chemical potentials of As and Ga vary over the thermodynamically allowed range. This result indicates that the rate of self-diffusion depends strongly on the surface-annealing conditions.

Coherent propagation of quadrupole polaritons in ${\mathrm{Cu}}_2$O is demonstrated by time-resolved spectroscopy. This manifests itself in a strong distortion of the temporal shape of a picosecond optical pulse which is in resonance with the 1S exciton polariton. Oscillations with time-dependent period in the transmitted light intensity are quantitatively explained as resulting from quantum beats between the two branches of the exciton polariton. The analysis yields the homogeneous linewidth and oscillator strength.

The creation of metastable dangling-bond defects in hydrogenated amorphous silicon subjected to short, intense laser pulses is investigated. It is found that pulse excitation leads to an order-of-magnitude increase in the defect creation rate compared to continuous illumination with the same average photon flux and photon energy. This implies that metastable-defect formation depends superlinearly on the density of photoexcited carriers. The much larger defect creation rate in the case of pulse excitation allows us to clarify the origin of saturation effects in the metastable-defect density, that are important for an assesment of the long-term conversion efficiency of amorphous-silicon solar cells.

Real-space-transfer (RST) transistors are studied theoretically. In a symmetric configuration, with no voltage applied between the channel electrodes, we find anomalous steady states in which the RST is driven by the fringing field from the collector electrode. Some of these states are unconditionally stable and hence accessible experimentally. Our study elucidates the formation of hot-electron domains, which is shown to be a discontinuous process that passes the control of electron heating from the drain to the collector. Multiply connected current-voltage characteristics are predicted.