The time development of diffractive scattering of picosecond light pulses from optically induced gratings in absorbing liquids is studied experimentally. Scattering begins quickly (in picoseconds) in saturable absorbers, but the scattering (stimulated thermal scattering) in a nonsaturable absorber requires many nanoseconds to develop. This resolves a discrepancy between theory and a previous experiment on stimulated thermal scattering.

The first detailed study of the critical exponent of phase separation, ${\beta }_{\mathrm{BM}}$, in a metallic binary liquid is reported. High-precision electrical resistivity measurements made on a Ga-Hg mixture of critical composition allowed the determination of ${\beta }_{\mathrm{BM}}$, which was found to be 0.335 ± 0.005 in the reduced temperature interval ${10}^{-4\mathrm{}}<~\epsilon <~{10}^{-2\mathrm{}}$.

Square planar complexes of platinum are shown to have high, possibly metallic conductivity along one axis due to overlap between $d_{z^2}$ orbitals of platinum in two valence states. The room-temperature Seebeck effect is small and positive which is interpreted as caused by a degenerate gas of holes.

We present experimental evidence that the structural transformation observed in ${\mathrm{Nb}}_3$Sn is first order, as predicted by theories which invoke a band Jahn-Teller mechanism for the lattice instability. The magnitude of the spontaneous lattice distortion at the transition temperature is in excellent agreement with the theory.

The attenuation length $l$ for photoelectrons excited in aluminum by 584-Å photons has been determined and found to lie in the range $4<~l<~12.8$ Å. The determination was made by analyzing the relative photoemissive yield as a function of angle. The method also provides an accurate means of obtaining the film thickness and index of refraction of aluminum from photoemission measurements alone.

Clean vacuum-deposited films of sodium were found to exhibit a work function of approximately 2.75 eV. Modification of the surface-plasmon frequency due to sulfur surface contamination was observed. The new value of the work function was shown to be due to a lack of surface contamination.

The rotation of ${\mathrm{Er}}^{3+}-\mathrm{F}_i^{}{}_{}{}^{-}$ dipoles in Ca${\mathrm{F}}_2$ was studied by the ionic thermocurrent (ITC) technique. Relaxation peaks at 138 K ($E=0.380\mathrm{}$ eV, ${\tau }_0=2\mathrm{}\times {10}^{-13\mathrm{}}$ sec) and 54 K ($E=0.167\mathrm{}$ eV, ${\tau }_0=3\mathrm{}\times {10}^{-15\mathrm{}}$ sec) were observed, and it is proposed that these are produced by the reorientation of the tetragonal complex (nearest-neighbor interstitial fluorine) and the trigonal complex (next-nearest-neighbor interstitial fluorine), respectively. Twidell recently reported inducing movement of the interstitial fluorine with uv light and his results are compared with the effects on the ITC spectrum caused by uv and by electron irradiation at low temperature.

A microwave nonlinear susceptibility analogous to the optical and electro-optical nonlinear susceptibilities is investigated in a number of acentric ferroelectric and semiconductor crystals. Contributions from ionic nonlinearities result in enormously larger nonlinear coefficients in some materials than any known for the optical or electro-optical effects. An interpretation is presented in terms of a relationship between the nonlinear coefficients and the electronic and ionic linear susceptibilities.

When a thin conducting film in the quantum-size-effect region is placed in a strong magnetic field, the electronic motion becomes three-dimensionally quantized. Simple analyses are presented to show that the magnetization and the differential susceptibility may undergo unusual transitions between positive and negative values.

Proton-proton and proton-neutron quasielastic scattering-process contributions were measured simultaneously at a proton energy of 12 MeV with ${\theta }_{1p}=-{30}^{\circ }$, ${\theta }_{2p}={\theta }_n={30}^{\circ }$. The ratio of the peak cross sections ${\left(\frac{{\sigma }_{\mathrm{np}}}{{\sigma }_{\mathrm{pp}}}\right)}_{\exp }$ was found to be 2.0 ± 0.2, while the simple impulse approximation predicts ${\left(\frac{{\sigma }_{\mathrm{np}}}{{\sigma }_{\mathrm{pp}}}\right)}_{\mathrm{imp}}=1.3\mathrm{}$. No Coulomb effects were found to be significant.

From a study of the reaction ${\mathrm{C}}^{12}({\mathrm{O}}^{16},{\alpha }_1){\mathrm{Mg}}^{24}\left({\alpha }_2\right){\mathrm{Ne}}^{20}$, spins and parities have been measured for states in ${\mathrm{Mg}}^{24}$ at the following excitation energies (in MeV): 12.10 ($4^{+}$), 12.45 ($7^{-}$), 13.07 ($5^{-}$), 14.41 ($4^{+}$), 16.07 ($6^{+}$), and 16.59 ($6^{+}$). Branching ratios were measured for several states in ${\mathrm{Mg}}^{24}$ with $13<~E_{\mathrm{exc}}<~23$ MeV decaying to the following states in ${\mathrm{Ne}}^{20}$: $0^{+}$ (ground state), $2^{+}$ (1.63 MeV), and $4^{+}$ (4.25 MeV). These results permit the elimination of several postulated structures for the states in question.

We report on the analysis of the reaction ${\pi }^{+}n\to {\omega }^{0}p$ at $6.95 \frac{\mathrm{GeV}}{c}$. The absence of a dip in the differential cross section at $t\simeq -0.6\mathrm{} {\left(\frac{\mathrm{GeV}}{c}\right)}^2$ and the nonzero values for the ${\omega }^0$ spin-density matrix element ${\rho }_{00}$ for $\mathrm{}\left|t\right|<1.4\mathrm{} {\left(\frac{\mathrm{GeV}}{c}\right)}^2$ indicates that an unnatural-parity contribution to this process is still important at this energy. A simple Regge-pole model is found to represent the general form of the data.

In the interaction of a high-energy particle with a proton or nucleus, the recoil spectrum of the target at very low momentum transfer is related simply to the total cross section of the incident particle with the photon. Estimates of the size of the effect plus recent developments in low-recoil techniques suggest that measurement of the photon-photon as well as the $\pi$- and $K$-photon cross sections may be possible.

We present strong theoretical evidence for the existence of highly inelastic $I=0\mathrm{}$ $K-N$ ($Z^{*}$) resonances in the $S_{\frac{1}{2}}$ and $D_{\frac{3}{2}}$ states at c.m. energies near 1830 MeV with widths of about 100 MeV.

We have observed an $\overline{\Omega }$ event. The $\overline{\Omega }$ is produced in the reaction $K^{+}d\to \overline{\Omega }\Lambda \Lambda p{\pi }^{+}{\pi }^{-}$ at $12 \frac{\mathrm{GeV}}{c}$, and decays via the mode $\overline{\Omega }\to \overline{\Lambda }{K}^{+}$. The fitted mass for this particle is $M_{\overline{\Omega }}=1673.1\mathrm{}\pm 1.0$ MeV. The $\overline{\Omega }$-production cross section is of the order of 0.1 μb.

We have measured the effective-mass spectrum of $K^{-}K_s^{}{}_{}{}^0$ particles produced in the forward direction in the reaction ${\pi }^{-}+p\to K^{-}+K_s^{}{}_{}{}^0+p$ at $20.3 \frac{\mathrm{GeV}}{c}$. A broad peak correponding to the $A_2$ meson is seen. The shape is fitted well by a single Breit-Wigner curve. A double-pole formula does not fit the data. A narrow peak in the $K^{-}{K}^0$ spectrum is seen at 1.425 GeV.

We have measured dc-induced optical second-harmonic generation by a focused laser beam; we verify the predicted dependence on geometric and physical parameters, thus providing a novel method of probing the confocal parameter at the laser focus. In addition, we have deduced values of ${\chi }_{\mathrm{yyyy}}(-2\mathrm{}\omega ;0,\omega ,\omega )$ for the inert gases, and we find good general agreement with various other data.

Zeeman splitting of the methane 2947.912-${\mathrm{cm}}^{-1\mathrm{}}$ $F_1^{}{}_{}{}^{\mathrm{}\left(2\right)\mathrm{}}$ line was studied. The $g$ factor of the rotational magnetic moment of methane was measured to be $g_J=+0.311\mathrm{}\pm 0.006$ and it was found that $g_J({\nu }_3=1)$ is equal to $g_J({\nu }_3=0)$. A Doppler-generated "level-crossing" saturated absorption signal was observed and is described.

It is found that ultrashort pulses in a high-gain 3.51-μm xenon laser propagate through the amplifying medium at a velocity less than the vacuum speed of light by as much as a factor of 2.5. The pulse velocity is a function of the gain and agrees with the group velocity.

The equilibrium configuration of a neutralized electron beam is calculated, including the self-field (parallel to the beam) generated by the beam itself. The resultant equilibrium configuration allows an arbitrary current to be carried by the beam, the motion of electrons being unimpeded by the self-magnetic field. Electrons in this configuration travel almost parallel to the magnetic field; thus, the synchrotron radiation can be minimized. It is suggested that this type of configuration opens up the possibility of low-loss electron coils and, in particular, is useful for fusion reactors.