Measurements of the back reflection from laser-produced plasmas have been carried out for laser intensities of up to 1.5×${10}^{16}$ W/${\mathrm{cm}}^2$ with pulse durations of 120 psec using spherical low-$Z$ targets. The reflectivity of the plasma increases with incident intensity but saturates at a value of 10%. The intensity-dependent reflectivity is attributed to stimulated Brillouin scattering.

Two-dimensional simulations of laser-plasma interactions in inhomogeneous media have been performed and clearly demonstrate that inhomogeneity effects can be strongly stabilizing for backscatter instabilities but may not be for sidescatter. The nonlinear evolution of the sidescatter is followed and indicates the possibility of very strong anomalous scattering of the incident laser light.

We solve exactly the temporal evolution and spatial dependence of a three-wave parametric instability in an inhomogeneous plasma. An initial fluctuation develops into a pulse and grows initially with the same growth rate as it would in a homogeneous plasma. Growth continues until convection saturation occurs. The pulse broadens as it grows and eventually assumes the form of a totally amplified region flanked by two shock fronts. Effects of damping are also discussed.

The operator algebra and an identity in the statistical mechanics of fluids are used to demonstrate that the cumulant average of arbitrary products of appropriate combinations of local fluctuating energy and density are scale and conformal covariant at the critical point. These combinations are uncorrelated and are found by diagonalizing a matrix whose elements are energy and density derivatives of pressure-density and pressure-energy correlations. The eigenvalues are the dimensions of the appropriate variables.

We derive the equations describing the decay of an intense, coherent electromagnetic wave into a backscattered electromagnetic wave and a plasma wave in an inhomogeneous plasma. The plasma wave and scattered electromagnetic wave are trapped in the vicinity of their cutoffs near ${\omega }_p=\frac{{\omega }_0}{2}$. The resulting temporally growing instabilities may explain the strong heating and the blowoff observed in recent computer simulations of Raman scattering.

The temperature dependence of the bend elastic constant of N-$p$-cyanobenzilidene-$p-n$-octyloxyaniline near the smectic-$A$—nematic transition temperature $T_c$ is found to obey the power law ${(T-{T_c}^{*})}^{-{\gamma }_3}$ with classical values for ${\gamma }_3$ in purer samples. Deviations from this value are discussed. Scanning calorimetry indicates that for purer samples the transition is either weakly first order or a $\lambda$ transition.

We have observed anomalously rapid relaxation of dipole-dipole energy in mixed-state superconducting vanadium. We show that spin diffusion driven by an inhomogeneous magnetic field uses spin-spin energy as a heat sink. Coupled differential equations are proposed for magnetization and spin-spin energy, and the diffusion coefficient is inferred from our measurements. It is concluded that spin diffusion cannot be a relaxation mechanism for magnetization in the mixed state, as previously assumed.

From field-ion microscope kinetic and equilibrium experiments with rhenium adatoms on W(110) planes it is found that the interaction potential energy between two adatoms exhibits an oscillatory behavior. The cohesive energy between two adatoms is very small, only ∼0.16 eV at the closest separation. These observations are in general agreement with the indirect adatom interaction models as proposed and discussed by various investigators.

Thermal Green's-function methods are used to solve the problem of a Jahn-Teller ion in an $E$ state coupling to the phonon continuum. The main results of Ham, previously derived for a molecular complex model, are firmly established for the phonon continuum model.

From positron lifetime measurements in seven powders of Fe, Co, Ni, and W, the positron diffusion constant in metals at 300°K is found to be $D_{+}=(1.0\mathrm{}\pm 0.5)\times {10}^{-2\mathrm{}}$ ${\mathrm{cm}}^2$/sec. This agrees with a theory based on positron-electron scattering. Evidence is presented that positrons are trapped in metal surface states.

Analytic results are derived for the surface properties of jellium. The surface potential relative to its bulk value is determined exactly in terms of the bulk properties of the uniform electron gas. This result is independent of any assumption concerning the electron energy density functional in an inhomogeneous system and depends only on the energy density in the homogeneous solid. We discuss the basic inapplicability of dispersiontype calculations of the surface energy.

Spin-correlation times in Ni are derived independently from perturbed angular correlation and neutron scattering experiments just above the Curie point. A comparison of these times shows that the usual form of the van Hove function does not apply for reduced temperatures $\epsilon <{10}^{-2\mathrm{}}$.

We report a search for quasistable particles with anomalous charge or large mass produced by the interaction of 300-GeV protons at the National Accelerator Laboratory. Analyses of energy losses in a counter telescope lead to cross-section limits of ${10}^{-35\mathrm{}}$ ${\mathrm{cm}}^2$ for particles with charges of $\frac{e}{3}$ and $\frac{2e}{3}$ and 5×${10}^{-31\mathrm{}}$ ${\mathrm{cm}}^2$ for charge-$\frac{4e}{3}$ particles. Time-of-flight measurements gave cross-section limits of about ${10}^{-31\mathrm{}}$ ${\mathrm{cm}}^2$ for the production of massive charged particles.

Molecular vibrational excitations by charged-particle impact are investigated within the Glauber-theory approach. Theoretical results for electron-${\mathrm{H}}_2$ scattering give good agreement with experimental data. We study the physical effects responsible for the structures in the differential cross section.

X rays emitted during the radiative capture of target electrons into the $K$ shell of fast and highly stripped projectiles were observed. When using targets with strongly bound electrons, a high-energy x-ray tail was also found; this new process is a type of electron bremsstrahlung. The cross sections for both these processes can be explained quantitatively.

The effect of velocity-changing collisions on the optical phase memory of coherently prepared molecular gas samples is examined by the method of Stark-pulse switching. Experiments are interpreted through the solution of a transport equation, which extends the earlier Fokker-Planck description known both in NMR and in Dicke line narrowing. The magnitude of a characteristic velocity jump for binary molecular collisions and its cross section are thereby obtained.

A novel autoacceleration mechanism was used to double the particle energy in a pulsed relativistic electron beam. This mechanism increases electron kinetic energy at the expense of pulse duration. Acceleration is accomplished by passing the beam through a cavity structure inserted into a conventional drift tube. Experimental results showed that the mean electron kinetic energy was increased from about 0.5 to 1.0 MeV, while the beam duration decreased from about 50 to 25 nsec. The total energy efficiency of the process was approximately 75%.

Parametric excitation of longitudinal plasma oscillations can occur when a plasma is simultaneously irradiated by two laser beams whose frequencies differ by $\left(\frac{2}{n}\right){\omega }_{\mathrm{pe}}$, $n=1, 2, 3, \cdots$, where ${\omega }_{\mathrm{pe}}$ is the electron plasma frequency. We examine (i) the effect of a frequency mismatch on the excitation of the principal mode, (ii) the mode coupling in an inhomogeneous plasma, and (iii) the radiation absorption efficiencies.

Plasma heating due to a high-frequency electric field near the electron cyclotron resonance is investigated in a toroidal plasma confinement device, the FM-1 spherator. It is observed that electrons and ions are heated "anomalously" when the incident high-frequency field exceeds a threshold value. Above the same threshold the parametric decay instability of upper and lower hybrid waves takes place. We investigate the effect of the decay instability and plasma heating on the confinement time.

Using a modified form of the model potential proposed by Kobayashi and McMillan to account for spatial ordering in liquid crystals, we calculate via mean-field theory a phase diagram and thermodynamic properties for liquid crystals including the isotropic, nematic, and smectic-$A$ phases. The results, as expected on purely physical grounds, are shown to give rise to excellent qualitative and quantitative agreement with experiment.