The spatial distribution and the dynamics of Cs atoms in a 1D optical molasses are probed by measuring the absorption (or amplification) spectrum of a weak laser beam. Narrow (35–50 kHz) Raman lines give access for the first time to the frequency and to the damping of the atom’s oscillation in the potential wells associated with light shifts. A narrower (8 kHz) Rayleigh resonance demonstrates the existence of a large-scale spatial order of the atoms, presenting some analogy with an antiferromagnetic medium.

The lowest vibrational energy levels of the ${\mathit{I}}^1$${\mathrm{\Sigma }}^{\mathrm{-}}$ and ${\mathit{D}}^1$Δ states of CO, which lie approximately 8 eV above the ${\mathit{X}}^1$${\mathrm{\Sigma }}^{+}$ ground state, are predicted to have very long radiative lifetimes, in excess of 1 s for electric dipole transitions. These states cannot predissociate and the couplings with levels of the ${\mathit{A}}^1$Π state are very small. There is, therefore, the possibility of using the V=0 levels of the ${\mathit{I}}^1$${\mathrm{\Sigma }}^{\mathrm{-}}$ and ${\mathit{D}}^1$Δ states as reservoirs for highly energetic molecules. In order to encourage experimental studies, methods are proposed for populating the v=0 levels of the ${\mathit{I}}^1$${\mathrm{\Sigma }}^{\mathrm{-}}$ and ${\mathit{D}}^1$Δ states, including stimulated emission from the ${\mathit{W}}^1$Π state.

We calculate the dissociation of ${\mathrm{H}}_2^{+}$ in intense short pulsed laser fields for a variety of wavelengths and a wide range of initial vibrational states (v=0–14). While the low-v levels achieve 100% dissociation in the leading edge of the pulse, for high v there is an onset of stabilization, and significant [(5–50)%] population remains in bound vibrational states throughout the entire pulse. The dissociation is incomplete, and a coherent distribution of excited vibrational states is formed. This survival effect can be attributed to the trapping of portions of the initial vibrational wave packet in transient laser-induced potential wells.

We present new experimental results for the angle and energy resolved backscattering of positrons and electrons from Al and Au at oblique incident angles. For ${\mathit{e}}^{+}$ on Au, and both ${\mathit{e}}^{\mathrm{-}}$ and ${\mathit{e}}^{+}$ incident on Al, evidence for specular scattering is observed. For positrons we find excellent agreement between these data and Monte Carlo simulations based on the Penn dielectric function.

Electrons are accelerated by large amplitude electron plasma waves driven by counterpropagating microwaves with a difference frequency approximately equal to the electron plasma frequency. Energetic electrons are observed only when the phase velocity of the wave is in the range 3${\mathit{v}}_{\mathit{e}}$<${\mathit{v}}_{\mathrm{ph}}$<7${\mathit{v}}_{\mathit{e}}$ (${\mathit{v}}_{\mathrm{ph}}$ was varied 2${\mathit{v}}_{\mathit{e}}$<${\mathit{v}}_{\mathrm{ph}}$<10${\mathit{v}}_{\mathit{e}}$), where ${\mathit{v}}_{\mathit{e}}$ is the electron thermal velocity, (${\mathit{kT}}_{\mathit{e}}$/${\mathit{m}}_{\mathit{e}}$${)}^{1/2}$. As the phase velocity increases, fewer electrons are accelerated to higher velocities. The measured current contained in these accelerated electrons has the power dependence predicted by theory, but the magnitude is lower than predicted [B. I. Cohen et al., Nucl. Fusion 28, 1519 (1988)].

Essential experimental features of sawtooth crashes are not explained by existing theories, especially the fact that ${\mathit{q}}_0$ remains well below unity throughout the sawtooth cycle. Here, a model consistent with experimental results is presented. The model considers the sawtooth crash as involving full reconnection of the magntiude field lines, leaving ${\mathit{q}}_0$<1. It leads to stronger plasma redistribution than the previous reconnection model; however, q(r) may remain almost unchanged. States with ${\mathit{q}}_0$ well below unity are shown to be possible results of different types of sawtooth crashes.

Scanning tunneling microscopy (STM) and high resolution low-energy electron diffraction measurements on vicinal (stepped) Si(111) surfaces reveal mixtures of single- and triple-layer-height steps, with the density of triples increasing with total step density. The diffraction signature of the step mixtures is an incommensurate spacing; however, the STM data show no periodic sequence of singles and triples. Instead, there is a random sequence with specific ratios of the lengths of terraces bounded by steps of different heights, quantitatively consistent with the energetic ground state for elastically interacting steps.

The behavior of correlation functions in the two-dimensional incommensurate phase with quenched impurities is studied using the Bethe ansatz solution of the corresponding replicated model. It is shown that the incommensurate phase containing many solitons remains critical even in the presence of impurities; the correlation functions have a power-law asymptotic behavior. The system with impurities even remains in the universality class of the ‘‘clean’’ problem. It is shown that the interaction with impurities affects scaling dimensions of correlation functions; they are calculated from the exact solution and depend continuously on the disorder.

Remarkably rapid Brownian motion of helium bubbles in aluminum alloyed with very low concentrations of lead and of indium has been observed in situ by hot-stage transmission electron microscopy. Bubble diffusion is enhanced as the impurity coats the bubble surfaces at annealing temperatures above the melting point of the impurity. The bubble diffusion coefficients calculated from video images of the bubble motion, and the corresponding surface diffusion coefficients, are orders of magnitude larger than diffusion coefficients determined from helium bubble growth experiments in pure aluminum.

We measured the isobaric thermal expansion coefficient ${\mathrm{\beta }}_{\mathit{P}}$ near the superfluid transition of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in an aerogel along six isobars between 3 and 24 bars. The data yield the specific-heat exponents α and α’ and amplitude ratio A/A’. Fits by power laws in t≡T/${\mathit{T}}_{\mathit{c}}$-1, where ${\mathit{T}}_{\mathit{c}}$ is the transition temperature, produced α≃-0.6 and α’≃-1.0≠α. Including an analytic background a×t permitted α=α’≃-0.59, but required a very large coefficient a and yielded A’/A≃0. The exponents are inconsistent with that of ${\mathrm{\rho }}_{\mathit{s}}$ and hyperscaling in three dimensions.

Using dimensional analysis, we show that the variable-range-hopping resistivity ρ of disordered systems with Coulomb interactions obeys the scaling form ln(ρ/${\mathrm{\rho }}_0$)=Af(T/${\mathit{T}}_{\mathit{x}}$), where f(x) is a universal function and A and ${\mathit{T}}_{\mathit{x}}$ are sample-dependent constants. A simple heuristic calculation in three dimensions yields an explicit form, for f(x), which exhibits a smooth-crossover from the Mott (f∝${\mathit{x}}^{\mathrm{-}1/4}$) to the Efros-Shklovskii (f∝${\mathit{x}}^{\mathrm{-}1/2}$) behaviors. Data on five different samples of compensated n-type CdSe are shown to collapse onto this single function.

The 1S to 1P excitonic transition in Cd(S,Se) quantum dots in glass was observed as a distinct peak in an infrared absorption spectrum (2–5 μm) induced with a subpicosecond visible laser pulse (585 nm). The temporal behavior of the induced absorption at the peak indicates that the 1P to 1S exciton relaxation is faster than 0.7 ps and the 1S exicton lifetime is about 20 ps. The 1S to 1P transition energy allows us to determine the eigenenergies for both electron and holes as well as the effective mean radius of dots. Direct transmission electron microscopy examination independently confirms the sizes of the quantum dots.

We investigate the phase diagram for a general structure (e.g., an interface) subject to both a periodic pinning potential and pinning to impurities. We find generically three phases—a flat phase which reveals strong glassy behavior, a rough glassy phase, and a weakly disordred flat phase. Experimental realizations include the pinning of Bloch walls and the problem of flux lines in layered superconductors when the applied field is parallel to the layers.

A new method of measuring the dynamics of magnetization at arbitrary magnetic field is presented. It is illustrated by measuring the spin-lattice relaxation rate in paramagnetic ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te in magnetic fields up to 25 T. At low fields, the spin-spin interaction of the Mn spins dominates the relaxation process; however, at high fields the relaxation of isolated spins can be observed. Among the spin clusters playing an important role as fast relaxation centers, exchange-coupled nearest-neighbor Mn pairs are identified, suggesting an important mixing of their states.

The absorption cross-section profile of large charged clusters is measured by a new procedure based on multistep photoabsorption experiments. Comparison is done with the predictions of classical and quantum treatments. In light of these results, size trends in the optical properties of alkali clusters are discussed.

Ultrafast recombination of holes with shallow acceptors in a III-V semiconductor is directly observed for the first time, by means of picosecond infrared spectroscopy. Neutral impurities in p-doped GaAs at low temperature are photoionized by picosecond infrared excitation. The recombination of free holes with negatively charged acceptors—monitored via absorption changes below the band edge—occurs on a time scale of several tens of picoseconds, following a nonexponential kinetics. Emission of longitudinal-optical phonons by the free holes is found to be the dominant mechanism of recombination.

The band gap of solid ${\mathrm{C}}_{60}$ is found to be 2.3±0.1 eV. The on-site molecular ${\mathrm{C}}_{60}$ Coulomb interaction (U) as determined from the KVV ${\mathrm{C}}_{60}$ Auger spectrum is found to be 1.6±0.2 eV. This value of U is shown to lead to Frenkel-type molecular excitons in the 1.5–2 eV range. These results lead us to suggest that doped ${\mathrm{C}}_{60}$ should be considered as a highly correlated system with U/W comparable to that in high-${\mathit{T}}_{\mathit{c}}$ cuprates and that stoichiometric ${\mathrm{K}}_3$${\mathrm{C}}_{60}$ is a Mott-Hubbard insulator with a gap of about 0.7 eV.

Quantum oscillations in the magnetization, periodic in inverse field (de Haas–van Alphen effect), have been observed in ${\mathrm{V}}_3$Si both above as well as below the superconducting critical field ${\mathit{B}}_{\mathit{c}2}$ of 17.95 T for fields along the [100] direction and at 1.5 K. The oscillations have the same frequency (±0.3%) in the two field regimes. It is shown by intercomparing the amplitudes that quantum oscillation measurements can be used to determine the field density distribution in the superconducting phase.

A new asymptotic behavior of reversible pseudo first-order binary chemical reactions is revealed by time-resolved fluorescence measurements of excited-state proton transfer. The asymptotic behavior is a power-law rather than the exponential decay expected from the chemical rate equations. Unlike the conclusion from mean-field approximations, the power seems to increase with concentration.

The concept of adiabatic invariance in one-dimensional Hamiltonian systems H(p,q;λ) is generalized to include the case when the time derivative of the slowly varying parameter λ is given by λ̇=f(H,λ)φ(q,p), where f and φ are arbitrary functions, and q and p are the canonical coordinates.