During intense C${\mathrm{O}}_2$-laser irradiation deep corrugations build up on liquid metals such as Hg, In, Sn, Al, and Pb. Spacing, orientation, growth, and decay of the corrugations are studied, by visible light diffraction; support is found for a model of stimulated scattering where the incident light parametrically decays into both the surface corrugation and a surface plasmon. Thermal evaporation supplies the nonlinearity. The instability provides polarization-dependent absorption and can be expected in laser-metalworking and laser-plasma situations.

The electrical and thermal properties of the divertor channel of tokamak plasmas are discussed in relation to $H$-mode discharges recently observed in neutral-beam-heated tokamak plasmas with divertors. The conditions for the existence of a thermal barrier and its effects on thermal and electrical conduction are analyzed, and the condition for effective line tying by the divertor plate is discussed.

It is shown that poloidal ring limiters are very effective in stabilizing ideal external kink modes in a tokamak. With one poloidal limiter all external modes are stable for $q_a>1\mathrm{}$. However, toroidal limiters have negligible influence on stability. Reversed-field pinches require a finite number of poloidal limiters (typically six) to stabilize the strong external kink modes that would result if the conducting wall were removed.

Conoscopic observations have been made on a mixture of potassium laurate, 1-decanol, and ${\mathrm{D}}_2$O in the discotic-uniaxial, biaxial, and cylindric-uniaxial nematic phases. The differences between the principal refractive indices have been measured, leading to a complete determination of the tensor order parameter in all the three phases. In the biaxial phase, the symmetric invariants of the order parameter are found to have a linear dependence on temperature, in good agreement with the prediction of the mean-field model.

An irreversible kinetic gelation model is studied by Monte Carlo simulations on a square lattice. By two different methods, it is found that the gel network is self-similar at the gel point. The fractal dimension $D$ is measured and it is compared with percolation and with other kinetic models of cluster formation. With use of scaling, the exponent ratios $\frac{\gamma }{\nu }$ and $\frac{\beta }{\nu }$ are obtained from the results for $D$.

New measurements of the damping $D_2$ of second sound in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ near $T_{\lambda }$ which are a factor of 5 more precise than previous results are reported. They span a wide pressure range, whereas previous data existed only at vapor pressure. The pressure dependence of $D_2$ agrees well with renormalization-group theory predictions, but the detailed temperature dependence differs slightly from that predicted on the basis of the presently available theory.

Continuous-wave nuclear magnetic resonance measurements have been performed on liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures of 5.0% (at 0, 10, and 20 bars) and 9.5% (at 10 bars) ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ between 0.3 and 25 mK. In the collisionless regime the NMR line is observed to shift and have a maximum in width, effects attributable to spin-wave excitations in the mixture and the first direct evidence for the existence of collective excitations in the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ Fermi systems. Analysis of the data yields the Fermi-liquid parameter ${F_1}^a$ for the 5%-${}_{}{}^3{}_{}{}^{}\mathrm{He}$ mixture.

Measurements of relaxation phenomena between liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ nuclei in small fluorocarbon particles are reported. Magnetic cross relaxation between the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ in the substrate and the liquid is observed in measurements between 1 K and 0.6 mK. The spin temperatures remain strongly coupled in magnetic fields up to 125 mT. Moreover it is observed that there is a decrease in magnetic relaxation time at the onset of superfluidity in the liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and that the thermal relaxation times are remarkably short at all temperatures.

A high-precision NMR technique was used to measure the magnetic susceptibility of bcc solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at several molar volumes over a temperature range well above the ordering temperature. The results resolve a long-standing inconsistency between high-magnetic-field pressure measurements and earlier magnetic susceptibility measurements, give new values of the Curie-Weiss temperature $\theta$ nearly a factor of 2 smaller than previous values, and suggest that $\theta$ follows a power-law volume dependence.

The excitation profile for solitons in trans-${\left(\mathrm{CH}\right)}_x$ was determined by measuring the strength of the photoinduced absorption as a function of the photogeneration source. The results demonstrate soliton photoproduction at energies well below the principal interband absorption edge. These data prove that charged soliton-antisoliton pairs are photogenerated directly (threshold $\hslash \omega =\frac{4\Delta }{\pi }$) assisted by quantum fluctuations in the ground state, as well as indirectly at higher energies ($\hslash \omega >~2\Delta$) via structural relaxation around electron-hole excitations.

Within a Peierls continuum description of the infinite polyyne chain $($$C\equiv C$$)$ it is found that the polymer possesses soliton excitations with charges $\pm 2e$, $\pm e$, and 0 and polaron states with charges $\pm e$, $\pm 2e$, and $\pm 3e$. An excitation ("polarexciton") consisting of an electron and a hole bound by lattice distortion is also found and may be photogenerated in the polymer.

Picosecond laser pulses are used to sequentially heat and probe the thermally induced reflectivity transients in copper, and the nonequilibrium heating of electrons to a temperature above that of the lattice is observed. The ability to temporally resolve electronic and lattice heating contributions is of considerable significance to thermomodulation spectroscopy of solids.

Measurements of electrical conductivity $\sigma$ as a function of temperature in the doubledonor system Si: P, As are reported. Data are related to a reduced concentration variable which is defined in terms of space filling by the interwoven impurity systems. The metalinsulator transition, when compared with those in Si: P and Si: As, appears to be unaffected by the additional vertical disorder introduced by the differing ionization energies of the two donors.

The spin-orbit interaction can mix electronic states of different orbital symmetry. By a special photoemission technique which makes use of optical spin orientation the degree of mixing is determined experimentally. As an example, valence-band states near the $\Gamma$ point of germanium are investigated.

Single-particle tunneling measurements have been used to study the paramagnetic, superconducting, and ferromagnetic phases of polycrystalline films of the reentrant superconductor Er${\mathrm{Rh}}_4$${\mathrm{B}}_4$. Anomalous features of the tunneling conductance in the ferromagnetic phase which persist into the superconducting state have been observed. These features seem intimately connected with the onset of ferromagnetism in the region of coexistence of ferromagnetism and superconductivity just above $T_{c^2}$.

The tomographic transform is combined with Susskind-like methods for lattice fermions to yield a new formulation with no multiplicity of species and with the usual discrete chiral symmetry.

The polarization of ${\Xi }^0$ and $\Lambda$ hyperons produced by 400-GeV protons interacting with a beryllium target has been measured in the projectile fragmentation region. The ${\Xi }^0$ polarization agrees in sign, magnitude, and kinematic behavior with that of $\Lambda$. The target dependence of these ${\Xi }^0$ and $\Lambda$ polarizations was also investigated with use of Cu and Pb targets.

Cross sections are reported for the excitation of Na atoms from the ground level to the $3p$ level by 1-25-keV incident ${\mathrm{H}}^{-}$ ions or ${\mathrm{H}}^0$ atoms. The cross section for excitation by incident ${\mathrm{H}}^{-}$ rises from 1.4×${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ at 1 keV to a maximum of 3.8×${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ at 15 keV and then falls to 3.6×${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ at 25 keV. The cross section for excitation by ${\mathrm{H}}^0$ falls from 1.3×${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ at 1 keV to 2.7×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ at 25 keV. These cross sections are compared with previously measured cross sections for excitation of Na by protons and electrons.

Optical dephasing rates ${T_2}^{-1\mathrm{}}$ of a dilute concentration of ${\mathrm{Nd}}^{3+}$ ions in a pure silica fiber have been studied from 0.05 to 1.0 K with use of two-pulse photon echoes. Echoes obtained by resonant excitation of ${\mathrm{Nd}}^{3+}$ into the metastable ${}_{}{}^4{}_{}{}^{}F_{\frac{3}{2}}^{}{}_{}{}^{}$ state from the ${}_{}{}^4{}_{}{}^{}I_{\frac{9}{2}}^{}{}_{}{}^{}$ ground state have yielded ${T_2}^{-1\mathrm{}}=1.3\mathrm{}\times {10}^{-6\mathrm{}}$ ${\mathrm{s}}^{-1\mathrm{}}$ at 0.1 K which follows a $T^{\frac{4}{3}}$ temperature dependence to 1.0 K. A crossover of ${T_2}^{-1\mathrm{}}$ to a $T^2$ temperature dependence above 1 K is inferred by comparison with earlier high-temperature linewidth measurements on this transition.

A toroidal array of racetrack-shaped coils whose major axes are alternately oriented vertically and horizontally ("Andreoletti coils") provides neoclassical confinement that is strikingly superior to a simple bumpy torus of similar aspect ratio but circular coils. For suitable parameters, the drift surfaces of deeply trapped and passing particles can be made concentric. At large minor radii, near the stabilizing ELMO rings, there exist closed, almost concentric drift surfaces for all pitch angles.