We have observed transitions to autoionizing states in Mg using two short optical pulses. Mg atoms are initially prepared in a high lying Rydberg wave packet with the first ps laser. A second ps laser is then used to excite the inner electron, producing an autoionizing state. The dependence of the transition probability on the delay between the two lasers shows that when the second laser is tuned away from the ionic resonance, the inner electron can make a transition only when the Rydberg wave packet is near the core.

Multiphoton detachment of ${\mathrm{Te}}^{\mathrm{-}}$ is studied utilizing two optical fields of wavelengths ∼694 and ∼1064 nm, respectively. Three-photon detachment is resonantly enhanced when the Raman condition is satisfied for coupling of the ${\mathrm{Te}}^{\mathrm{-}}$ 5${\mathit{p}}^5$ ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{3/2}$ and ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2}$ fine-structure states. The fine-structure splitting is determined to be 5004.7±0.2 ${\mathrm{cm}}^{\mathrm{-}1}$, which represents a 25-fold improvement over earlier measurements. The possibilities for extended spectroscopic measurements, as well as general perspectives for multiphoton experiments at high intensities, are briefly discussed.

Absolute cross sections have been measured for the first time for the electron-impact single ionization of the fullerene ions ${\mathrm{C}}_{60}^{+}$, ${\mathrm{C}}_{60}^{2+}$, ${\mathrm{C}}_{60}^{3+}$, and ${\mathrm{C}}_{70}^{+}$ as well as for double ionization of ${\mathrm{C}}_{60}^{+}$ ions at electron energies ranging from threshold up to 1000 eV. It is found that the cross sections ${\mathrm{\sigma }}_{1,2}$ for ${\mathrm{C}}_{60}^{+}$ and ${\mathrm{C}}_{70}^{+}$ ions coincide within error bars and, furthermore, that at energies greater than 60 eV the cross section ${\mathrm{\sigma }}_{2,3}$ for ionization of ${\mathrm{C}}_{60}^{2+}$ ions is larger than ${\mathrm{\sigma }}_{1,2}$. In addition, cross sections for fragmentation ${\mathrm{C}}_{60}^{+}$→${\mathrm{C}}_{56}^{+}$ and for fragmentation ionization ${\mathrm{C}}_{60}^{+}$→${\mathrm{C}}_{56}^{2+}$ are presented.

We have completed a new measurement of parity nonconserving (PNC) optical rotation near the 1.279 μm magnetic dipole absorption line in lead, improving earlier results on this line by a factor of 20. We find the ratio of the PNC E1 amplitude to the M1 amplitude to be scrR=(-9.86±0.12)×${10}^{\mathrm{-}8}$, consistent with theoretical predictions. Difficulties in the atomic theory of lead presently limit the extent to which our result tests the standard model of electroweak interactions. The amplitude of the nuclear spin-dependent PNC rotation is found to be less than 2×${10}^{\mathrm{-}2}$ of the nuclear spin-independent rotation.

Irradiating glass by intense light at frequencies ω and 2ω generates a semipermanent dc electric field in the glass that transforms the glass into a phase-method optical-frequency doubler. We map out this dc electric field over a wide variety of experimental conditions. We show that its symmetries are predicted by a theory based on the interference of competing multiphoton ionization channels.

A linear chain of atoms, interacting with anharmonic forces, one of whose end atoms is forced to vibrate harmonically, is studied as a simple model for kinetic friction between ideal crystalline solids. It is found that there is a transition, as a function of chain length and driving frequency between a regime in which there is dissipation (i.e., the internal energy increases as a function of time on the average) and one in which there is practically no dissipation. This suggests that there can be dissipationless sliding fro sufficiently small solids.

A critical analysis of the conformal approach to the theory of 2D turbulence is delivered. It is shown, in particular, that conformal minimal models cannot give a general turbulent solution, which should provide for constant fluxes of all vorticity integrals of motion.

We consider the viscous motion of an axisymmetric column of fluid with a free surface. The Navier-Stokes equation forms a singularity as the height of the fluid neck goes to zero. Close to pinchoff, the solutions have a scaling form characterized by a set of universal exponents. The shape of the neck and its velocity field is described by scaling functions, which we predict without adjustable parameters.

We find the self-similar scaling behavior x∼${\mathit{t}}^{3/5}$,y∼${\mathit{t}}^{2/5}$ for the arms which form in radial Hele-Shaw flow with anisotropic surface energy, where x is the longitudinal and y is the transverse coordinate of each primary finger. We first obseve this by direct numerical simulation using a boundary-integral method. Then we analytically derive the scaling law and the full asymptotic shape, by combining a simple boundary-layer analysis with previous results on velocity selection.

The dynamical behavior of the surface tension of two initially immiscible phases on raising the temperature to a value greater than or equal to the critical temperature is studied using analytic techniques, mean field dynamical equations, Monte Carlo simulations, and molecular dynamics simulations. Distinct behavior is predicted in situations with a conserved order parameter and when no conservation law is operative. A novel scaling form is obtained for a system evolving to equilibrium at its critical temperature.

The vortex street behind a ring of circular cross section and large aspect ratio is investigated experimentally. Different modes of annular and helical vortex shedding are identified by phase and frequency measurements. Their stability domains overlap in a large interval in Reynolds number where mode selection depends on initial conditions only. A new instability of the vortex shedding process involving characteristic mode transitions has been observed. This instability can be explained in the context of a Ginzburg-Landau model by a mechanism resembling formally the Eckhaus instability of spatially periodic patterns.

The acceleration of a material interface by a shock wave generates an interface instability known as the Richtmyer-Meshkov instability. Previous attempts to model the growth rate of the instability have produced values that are almost twice that of the experimental measurements. This Letter presents numerical simulations using front tracking that for the first time are in quantitative agreement with experiments of a shocked air-${\mathrm{SF}}_6$ interface. Moreover, the failure of the impulsive model, and the linear theory from which it is derived, to model experiments correctly is understood in terms of time limits on the validity of the linear model.

The dynamics of plastic foils of different thicknesses which were irradiated with intense, approximately Planckian soft-x-ray pulses, have been investigated using a high magnification (80×), time-resolving extreme ultraviolet (95 or 205 eV) imaging technique for the first time. The experimental results are discussed and compared with hydrocode simulations.

We derive the fully relativistic Ohm’s law for an electron-positron plasma. The absence of nonresistive terms in Ohm’s law and the natural substitution of the four-velocity for the velocity flux in the relativistic bulk plasma equations do not require the field gradient length scale to be much larger than the lepton inertial lengths, or the existence of a frame in which the distribution functions are isotropic.

X-ray absorption fine structure (XAFS) measurements of mixed salts ${\mathrm{Rb}}_{\mathit{x}}$${\mathrm{K}}_{1\mathrm{-}\mathit{x}}$Br and ${\mathrm{RbBr}}_{\mathit{y}}$${\mathrm{Cl}}_{1\mathrm{-}\mathit{y}}$ at their congruent melting points compositions reveal that their actual structure buckles about the NaCl average structure with an rms angular deviation from collinearity of 7–9°. XAFS measures the buckling directly through three-body correlations, and verifies the homogeneity and randomness of the mixtures. The characteristic ionic sizes are found to be dependent on concentration, causing changes to 0.1 Å in interatom bond distances. A computer simulation based on the information from XAFS and diffraction displays the actual structure of the salts.

Details of the atomic structure for the Si(100)-(2×1) surface using UHV transmission electron diffraction are described. Reliability factor minimizations of the dynamical diffraction intensities establish conclusively the asymmetry in the structure. Fits performed using multilayer subsurface relaxations to match analytical strain solutions demonstrate the existence of long range subsurface strain fields extending up to six layers into the bulk.

The chemical and proximity dependence of electromagnetic interactions of various metallic bodies at nanometer separations is probed through photon emission from a scanning tunneling microscope. The role of local dielectric properties is determined and the strength of the electromagnetic coupling in the cavity between tip and sample is investigated. The experimental results compare well with model calulations and show the relative role of the dielectric functions of both electrodes as well as the influence of proximity.

Strain-induced symmetry changes in diamond have been observed in shock compression experiments. The experimental method utilizes time-resolved Raman spectroscopy to probe the diamond structure behind the shock front. Peak longitudinal stresses up to 50 GPa were achieved by uniaxial strain loading. Strain applied along the [100] and [110] directions is predicted to partially or completely lift the triple degeneracy of the ambient Raman line. The degenerate Raman line was observed to split in accordance with the predicted behavior. The observed changes, despite the large nonhydrostatic stresses, are reversible.

We present the first detailed numerical study of domain growth in the ordered phase of a 3D quenched random-field (RF) model. The nonconserved order parameter obeys the time-dependent Ginzburg-Landau equations. At late times, the scaling functions of the RF and pure systems are identical, placing them in the same universality class, as defined via the renormalization group. The domain size R(t) grows initially as ${\mathit{t}}^{1/2}$ and then crosses over to slow logarithmic evolution. This is interpreted as arising from a renormalization of the kinetic coefficient at short length scales and can be associated with a dangerously irrelevant operator at the zero-temperature fixed point.

We have studied, via x-ray scattering, the nematic to smectic-A (NA) translational ordering of the liquid-crystal–forming compound octylcyanobiphenyl (8CB) incorporated into the pores of a silica aerogel. We find that the aerogel dramatically alters 8CB phase behavior, eliminating the NA transition found at T=${\mathit{T}}_{\mathit{N}\mathit{A}}$=33.7 °C in bulk samples and replacing it by a short range smectic ordering having a correlation length which at ${\mathit{T}}_{\mathit{N}\mathit{A}}$ is ξ∼40 Å, much smaller than the aerogel pore and nematic domain size ${\xi }_{\mathit{p}}$∼200 Å. As T is lowered this smectic disorder is eliminated from the pores, ξ increasing continuously over a 20 °C range to saturate at ${\xi }_{\mathit{p}}$ for T<${\mathit{T}}_{\mathit{N}\mathit{A}}$-20 °C.