First observed visible harmonics of C${\mathrm{O}}_2$-laser—irradiated plane and microballoon targets are reported. For intensities >5×${10}^{14}$ W/${\mathrm{cm}}^2$, the harmonic production efficiency is constant over several visible harmonics with a cutoff at a high harmonic number. Two-dimensional particle simulations performed where there is a highly steepened density profile show a flat spectrum for high harmonics with a cutoff at the harmonic where the upper density shelf is underdense. Harmonics thus offer a means of measuring the upper density shelf and its dynamics.

The effects of anisotropic ion-wave damping in stimulated Brillouin scattering, including rescattering, are investigated. Anisotropy is shown to reduce substantially the limiting (infinite plasma) reflection even at modest levels of $\beta =\frac{{\nu }_{+}}{{\nu }_{-}}$, the ratio of the ion-wave-damping rates.

Mass separation in magnetized, highly ionized, rotating metal plasmas is described. Plasma rotation velocities up to 7.4×${10}^3$ m/sec with centrifugal enrichment of up to a factor of 2 for ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}$ were measured. Such enrichments are significantly in excess of values reported earlier.

The main phase transition in smectic liquid crystals of a hydrated phospholipid involves a Martensitic transformation driven by the molecular-conformation changes. This inhomogeneous shear transformation generates periodic crystallographic twins that appear as corrugations of the molecular bilayer sheets. The model accounts for the observed lipid shedding, hysteresis, double corrugation periodicities, and diffusion anomalies, and may account for other smectic herringbone structures.

For temperatures below phase separation of 1000 ppm ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in solid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, we measure a heat capacity $\gamma T$ for a pressure between melting of pure ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. Together with the confined sample geometry, this results in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ droplets ($\varphi \sim {10}^3$ Å) either dilute or pure depending on the phase diagram topology which is discussed theoretically. In the case of a pure ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ droplet, an anomalously high effective mass $\frac{m^{*}}{m}=10\mathrm{}$ is found, which could be explained by paramagnon effects enhanced by the confined geometry.

It has been discovered that the disordered material ${\mathrm{Ge}}_{1-x}{\mathrm{Au}}_x$ displays an unusual type of metal-insulator transition as the composition $x$ is varied. The onset of conductivity, as extrapolated to $T=0\mathrm{}$ K, is continuous, and thus the system has no "minimum metallic conductivity."

The free energy is calculated for the various phases possible in a superconductor containing a periodic array of magnetic ions with ferromagnetic interactions. Suggestions are made for experimental observation of coexisting superconductivity and long-range magnetic order.

$\gamma$-ray techniques have been used to measure the total cross section for populating the 1.78-MeV $2^{+}$ state in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ via the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ reaction at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=23-35\mathrm{}$ MeV. Unlike the highly structured back-angle elastic- and inelastic-scattering excitation functions, the integrated inelastic yield is found to vary smoothly with energy. The absence of structure in the total inelastic cross section does not support a resonance interpretation of the back-angle particle-scattering data.

Electronic Raman scattering on shallow donors in semiconductors is enormously enhanced when the incident photon energy approaches the fundamental exciton region. This excitonic resonance was observed for the first time and it was found that ${\sigma }_{\mathrm{peak}}\approx 5\times {10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$ for CdTe and GaAs in the $n=2\mathrm{}$ free-exciton resonance. The enhancement of ≳ ${10}^{10}$ over off-resonance excitation and the peculiar $n=2\mathrm{}$ exciton predominance are well described in a model of exciton-polariton-mediated light scattering.

Surface-enhanced Raman scattering from a layer of organic molecules adsorbed on aluminum oxide and covered by a controlled-roughness silver film has been studied. The molecule-silver distance dependence of the Raman-scattering enhancement by the surface was measured in four separate experiments. Large enhancements (∼${10}^3$) persist in our samples for molecule-silver separation as large as 100 Å, and thus the use of surface-enhanced Raman scattering is shown to be a viable technique for vibrational spectroscopy of a large variety of interface systems.

Measurements of time-resolved luminescence spectra of electron-hole liquid in Ge under $〈111〉$ uniaxial stress are reported. It is shown that these spectra present strong evidence that a novel phase separation recently predicted theoretically for this system does indeed occur. The critical ratio $x_c$ of the number of hot electrons to that of cold electrons below which the phase separation occurs is found to be 0.63 for a stress of 6.8 kg/${\mathrm{mm}}^2$.

It is shown that under certain conditions a superconductor with spin fluctuations (paramagnons) exhibits the same tunneling characteristics and thermodynamic properties as a superconductor with no paramagnons having the same electron-phonon interaction but scaled down, and an increased effective Coulomb interaction. The condition is that the paramagnon frequency be much higher than any phonon frequency. The effective anisotropy in the electron-phonon interaction is also shown to increase.

A new mechanism is described for the spin relaxation of photoelectrons in $p$-type semiconductors through the electromagnetic coupling to virtual photons. For the degenerate case the result approaches a limit independent of hole density and temperature, distinguishing this mechanism from all others that have been proposed. Experimental results on optically pumped Zn-doped GaAs (5×${10}^{17}$ to 2×${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$) are presented which confirm the existence of such a regime with ${\tau }_s\sim 1.5\times {10}^{-9\mathrm{}}$ s.

Dynamic nuclear polarization is observed when methyl groups in ammonium acetate at 4.2 K are converted between $E$ and $A$ spin-symmetry species by paramagnetic impurities whose Zeeman splitting is tuned to the methyl-group tunnel splitting. Further nuclear polarization is subsequently generated as the effect on resonant methyl groups is transferred to nonresonant ones by spin-symmetry diffusion. The time constant for the establishment of internal thermal equilibrium among the methyl groups is measured.

Spectra and angular distributions of neutrons in coincidence with light fragments produced in deep-inelastic collisions of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ on ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ at 204 MeV have been measured. A significant number of neutrons are emitted in the forward direction with beamlike velocities. Fits of detailed spectra and angular distributions were not possible if one assumed evaporation from accelerated fragments. This presents the first direct evidence for nonequilibrium neutron emission in deep-inelastic reactions.

The results of a test of general relativity with use of a hydrogen-maser frequency standard in a spacecraft launched nearly vertically upward to 10 000 km are reported. The agreement of the observed relativistic frequency shift with prediction is at the 70×${10}^{-6\mathrm{}}$ level.

Direct $\mathrm{CP}$ tests in neutrino oscillations require comparison of off-diagonal channels ${\nu }_{\alpha }\to {\nu }_{\beta }$ with $\mathrm{CP}$-conjugate channels ${\overline{\nu }}_{\alpha }\to {\overline{\nu }}_{\beta }$ (or with ${\nu }_{\beta }\to {\nu }_{\alpha }$ by assuming $\mathrm{CPT}$ invariance). For the three-neutrino case, it is shown that $\mathrm{CP}$-nonconservation effects are identical in all three available channels ${\nu }_e\leftrightarrow {\nu }_{\mu }$, ${\nu }_{\mu }\leftrightarrow {\nu }_{\tau }$, and ${\nu }_{\tau }\leftrightarrow {\nu }_e$, and argued that they could be large and measurable in meson factory experiments. Indirect $\mathrm{CP}$ tests include the correlation of average probabilities.

A parity-nonconserving (PNC) neutron-spin rotation, ${\varphi }_{\mathrm{PNC}}$, for neutrons passing through matter due, presumably, to the weak interaction is observed for the first time. For tin isotopes, the following values for ${\varphi }_{\mathrm{PNC}}$ in ${10}^{-6\mathrm{}}$ rad/cm are found: ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$, +0.48±1.49; ${}_{}{}^{117}{}_{}{}^{}\mathrm{Sn}$, +36.7±2.7; and natural Sn, +4.95±0.93, with the positive sign corresponding to a right-handed rotation about the momentum. Evidence in ${}_{}{}^{117}{}_{}{}^{}\mathrm{Sn}$ for a larger total cross section for positive-helicity neutrons than for negative-helicity ones is also reported.

The polarization and $Q^2$ dependence of muoproduced $\psi \to {\mu }^{+}{\mu }^{-}$ have been analyzed in a magnetized-steel calorimeter at Fermilab. The reaction ${\gamma }_{V}N\to \psi N$ is found to be helicity conserving. Even after allowance for possible $Q^2$ dependence of the decay angular distribution, the $\psi$ muoproduction cross section falls more steeply in $Q^2$ than predicted by $\psi$ dominance.

Calculations made with use of a new relativistic theory of nuclear matter which allows for negative-energy components in the nucleon wave function introduce a major modification in the saturation curve for nuclear matter. For example, a boson-exchange potential which saturates at over twice the empirical density and yields a binding energy of about 23 MeV per particle is brought into general agreement with the empirical data when relativistic effects are included. This analysis indicates that nuclear matter should be treated as a relativistic system.