The prediction of squeezed optical pulses in single-mode fibers utilizing the Kerr effect has recently been verified for ultrashort solitonlike pulses [M. Rosenbluh and R. M. Shelby, Phys. Rev. Lett. 66, 153 (1991)]. We present a substantial modification of the existing quantum theory to account for Raman quantum noise, which is the limiting factor in generating wide-band squeezing for ultrashort pulses.

A very stringent test of low-energy electron-atom collision theory is made in the most favorable energy regime for the close-coupling approximation. Data are presented as exchange asymmetries in angle-resolved elastic scattering of spin-polarized electrons from spin-polarized sodium atoms. Data are reported for two incident energies, 1.0 and 1.6 eV, both of which are below the first excited-state threshold. The angular range is 20–142.5°. The close-coupling approximation is found to give excellent agreement with experiment at both energies.

Photoelectron spectra of helium have been measured at different angles and at various energies above the double-ionization threshold up to 120 eV to investigate the behavior of the energy and angular distributions, of shake-off electrons. Both energy and angular distributions clearly show a U-shaped profile which turns to a flat curve near threshold pointing to a uniform intensity distribution over the kinetic energy for all angles in this excitation energy regime. Our results for the angular-distribution asymmetry parameter indicate qualitative agreement with theoretical predictions but fail to provide them quantitatively.

The nonlinear beam dynamics of transverse betatron oscillators were studied experimentally at the Indiana University Cyclotron Facility Cooler Ring. Particles were kicked onto resonance islands and the properties of these islands were studied. The island tune was determined with high precision by Fourier analyzing the spectrum containing the island oscillations. The island width was estimated based on a single-resonance model. The Hamiltonian of particle motion near a resonance condition was thus deduced.

Freely evolving two-dimensional turbulence is studied experimentally, in thin layers of electrolyte. The density of vortices, their mean sizes, and the average separation between them are measured during the decay phase. Power laws are observed, and the corresponding exponents are found in good agreement with a recent analysis of Carnevale et al.

A numerical method, based on a discrete Boltzmann equation, is presented for solving the equations of magnetohydrodynamics (MHD). The algorithm provides advantages similar to the cellular automaton method in that it is local and easily adapted to parallel computing environments. Because of much lower noise levels and less stringent requirements on lattice size, the method appears to be more competitive with traditional solution methods. Examples show that the model accurately reproduces both linear and nonlinear MHD phenomena.

Intense, soft-x-ray pulses, generated from separate laser-irradiated converters, were used to irradiate plane plastic foils. The x-ray heating was investigated by measuring the temperature histories of chlorinated tracer layers buried at different depths in the targets. The temperature diagonistic was a time-resolved extreme-UV absorption spectroscopy technique using chlorine L-shell transitions. The temporal temperature profiles were reasonably well reproduced by radiation-hydrocode simulations.

The first measurements of the opacity in a well characterized, hot, dense, laser-produced plasma are reported. Measurements of the absorption of x rays by 1 to 2 transitions in Al xii through Al viii have been made in a laser heated slab plasma at the measured temperature and density of 58±4 eV and 0.020±0.007 g/${\mathrm{cm}}^3$. The conditions in the plasma were determined to be reproducible, spatially uniform, and in nearly complete local thermodynamic equilibrium. The absorption spectra and the temperature-density data obtained provide an improved means for comparison with detailed atomic physics and opacity calculations.

We have measured the damping of a vibrating-wire resonator in liquid ${}_{}{}^3{}_{}{}^{}\mathit{A}$ down to temperatures of ${\mathit{T}}_{\mathit{c}}$/T of 7 at zero bar pressure in a field of 500 mT. A simultaneous measurement of the damping in the B phase is also recorded. The response in the A phase is found to follow an exponential temperature dependence and not a power law as might be naively expected. This effect is a consequence of the exclusion of a large fraction of the bulk low-energy excitations from a surface by the bending of the texture.

During the preparation of thin Au/In multilayers (0.39/1.2 nm, total thickness 48 nm) by ion-beam sputtering at 86 K, periodic interface reactions were observed by an Iin situP measurement of the electrical resistivity. The resulting phase was identified as amorphous ${\mathrm{Au}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$ with compositions x which were controlled by the choice of the individual Au and In layer thicknesses. The formation of these amorphous phases was restricted to a thin interface region (<6 nm) and, most important, could not be obtained by long-range diffusion of thick Au/In multilayers.

Light emission characteristics from the tunnel gap of a scanning tunneling microscope are used to elucidate the interaction of tunneling electrons with tip-induced plasmon modes on Ag, Au, and Cu surfaces. Enhanced redshifted spectra are observed in the tunneling regime. Model calculations of optical spectra in this range agree well with the experimental data. Isochromat spectra are used to demonstrate that the principal excitation process occurs via inelastic tunneling.

Scanning tunneling microscopy (STM) and first-principleds pseudopotential calculations are used to show that the equilibrium binding site for hydrogen on Ge(111)-c(2×8) is the rest-atom site. Our calculations show the hydrogen-rest-atom configuration is 0.7 eV lower in energy than the hydrogen-adatom configuration. Reaction at the rest-atom site causes very local rest-atom to adatom reverse charge transfer, and this site-specific chemistry is imaged directly using STM measurements in combination with these calculations.

The effect of further irradiation on 1×${10}^{15}$ or 6×${10}^{15}$ Kr/${\mathrm{cm}}^2$ implanted aluminum has been investigated by a channeling method with a 1 MeV ${\mathrm{He}}^{+}$ beam at room temperature. The post-implantation irradiation by the analysis beam enhanced the formation of epitaxial solid krypton precipitates. This result indicates that interstitial introduced during implantation play an important role in the formation of solid krypton for Kr implantation with high doses.

Coherent quasielastic neutron scattering has been used to investigate the character of the rotational dynamics in the high-temperature solid phase of ${\mathrm{C}}_{60}$. The observed scattering can be described by a model in which each molecule undergoes rotational diffusion which is uncorrelated with the motions of adjacent molecules. The rotational diffusion constant ${\mathit{D}}_{\mathit{R}}$ is (1.4±0.4)×${10}^{10}$ ${\mathrm{s}}^{\mathrm{-}1}$ at 260 K and (2.8±0.8)×${10}^{10}$ ${\mathrm{s}}^{\mathrm{-}1}$ at 520 K. The temperature dependence of ${\mathit{D}}_{\mathit{R}}$ is consistent with a thermally activated process having an activation energy of 35±15 meV.

We report on the direct synthesis of superlattices with lateral corrugation of the interfaces on (211), (311), and (111) GaAs substrates by moelcular-beam epitaxy. Reflection electron diffraction directly shows the formation of arrays of macrosteps during epitaxial growth. High-resolution transmission electron microscopy confirms the transfer of the surface structure to the GaAs/AlAs interface which results in distinct energy shifts in the luminescence of GaAs/AlAs multilayer structures. The surace structure gives rise to lateral quantum-size effects which result in increased exciton continuum energies, in strong exciton-phonon interaction, and in pronounced optical anisotropy.

We present theoretical evidence for strong excitonic effects at Si(111)2×1. On the basis of a self-consistent calculation of electronic states, excitons, and optical properties, which involves for the first time a realistic treatment of the screened electron-hole interaction, we find a gap between surface states of 0.75 eV, and an optical spectrum in quantitative agreement with expeiment. The exciton binding energy turns out to be ${\mathit{E}}_{\mathit{b}}$=0.3 eV. Higher excitonic states are not visible, due to the quasi-one-dimensionality of the surface states

Spin superlattices with alternating nonmagnetic and magnetic layers, in which a tunable spin-dependent potential exists, have been fabricated. We show that the ZnSe/${\mathrm{Zn}}_{0.99}$${\mathrm{Fe}}_{0.01}$Se system, in which field-induced spin splittings in both valence and conduction bands can become much larger than the residual zero-field potentials, exhibits spin superlattice behavior. Low-temperature magnetoreflectance experiments have been used to investigate the nature of these structures, verifying through field-dependent spin splitting and transition strengths that they are in fact true spin superlattices.

We present magneto-optical evidence for the formation of a magnetic-field-induced spin superlattice in modulated ZnSe/${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se structures. In the samples studied, the offsets in both the conduction band and the valence band are very small at zero magnetic field. When a magnetic field is applied, the large Zeeman splitting of the ${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se band edges overcomes the zero-field offsets and results in the formation of a spin superlattice in which spin states of both electrons and holes are spatially and periodically separated.

The resonances of a resonant tunneling structure are probed by a magnetic field applied parallel to the interfaces, which enables us to investigate the local band structure in k space. By rotating the magnetic field in the plane of the interfaces, the energy surface at constant ${\mathit{k}}_{\mathrm{\parallel }}$ is investigated. Using this technique we have studied differently strained Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ quantum wells; we see a large anisotropy of the energy levels, with the symmetry axes of light holes and heavy holes being rotated 45° with respect to each other.

First-principles electronic structure calculations were performed for a ${\mathrm{FeAl}}_{42}$ embedded cluster, representing an Fe impurity in Al. At the equilibrium positions of the Al first neighbors around Fe, obtained by total energy minimization, it was found that the impurity is nonmagnetic. This result is consistent with experimental observations and renders unnecessary a microscopic description based on spin fluctuations.