By means of low-energy cross-section measurements on ${\mathrm{He}}^3$-${\mathrm{He}}^3$, we derive an interatomic potential which has a minimum 3.4% deeper than that of ${\mathrm{He}}^4$-${\mathrm{He}}^4$. We demonstrate that the difference in the potentials is significant. The atomic-mass polarization effect is proposed as a possible explanation for the different potentials.

Inelastic photon scattering from ${\mathrm{I}}_2$ vapor was observed to change from resonance Raman scattering to resonance fluorescence as a single-mode argon laser was tuned through the 5145-Å gain profile. 3 orders of magnitude enhancement in the Stokes and the first-overtone intensities were measured in going from resonance Raman scattering to resonance fluorescence. The intensity distribution of the first 47 overtones is shown for the laser frequency coincident with the $43\to 0 P\left(12\right)\mathrm{}$ and $43\to 0 R\left(14\right)\mathrm{}$ transitions of $B^3\Pi _{0\mathrm{u}}^{}{}_{}{}^{+}\to X^1\Sigma _{0\mathrm{g}}^{}{}_{}{}^{+}$. The resonance Raman cross section of ${\mathrm{I}}_2$ compared with ${\mathrm{N}}_2$ was found to be 2.6 × ${10}^6$.

Nuclear magnetic resonance has been detected by following changes in the steady-state value of the longitudinal magnetization with a Josephson-junction magnetometer. Unlike previous fast-passage detection methods, this mode of detection gives a signal amplitude of $2M_0$ independent of the resonance linewidth and the rf power level. Maximum-intensity signals from room-temperature LiF have been obtained at 40 dB less power than that required for maximum signal using conventional adiabatic fast-passage detection methods.

Data on the capture and escape of negative ions in turbulent He II are reported for various pressures. The results are consistent with a revised version of Vinen's dimensional theory and previous experimental results on rotating He II. A model for vortex annihilation is developed which allows the turbulence theory to be expressed in terms of a single dimensionless constant which we measure.

Based on considerations of the rotating ideal Bose gas it is suggested that the quantized vortex lines can enter the superfluid contained in a rotating bucket through an adiabatic transformation of the ground state.

The Debye-Waller factor for bcc ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is calculated at $T=0\mathrm{}$ on the basis of a Hartree-Jastrow ground-state wave function by means of a cluster-expansion technique and is found to be a Gaussian function of the wave-vector transfer to within 1%. We discuss a possible reason for the large deviations from Gaussian behavior observed in recent neutron inelastic-scattering experiments.

An investigation of the high-energy, large-momentum-transfer neutron scattering from the low-density hcp and bcc phases of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has revealed scattered neutron groups with the same characteristics as those associated with single-particle scattering in liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. The observed groups of this type are independent of the crystallographic phase and of direction within the accuracy of this investigation. Such neutron groups have been observed at energies as low as 1.5 times the maximum phonon energy in the bcc phase.

The scattering function $S(Q,\omega )$ for inelastic neutron scattering from solid bcc ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been calculated including one- and two-phonon processes and their interference contributions. The intensity of the one-phonon line shows the anomalies found in recent experiments on solid and liquid helium. Indications for free-particle scattering are found at larger $Q$ values. Similarities between $S(Q,\omega )$ for the solid and the liquid are further explored and discussed.

For incident laser giant pulses the high conversion of laser light into Raman light limits the size of the beam diameter in liquid toluene, benzene, and in mixtures of benzene and C${\mathrm{S}}_2$. Computer calculations are in agreement with the experimental results.

Using light-beating spectroscopy, we observe the Rayleigh scattering from a smectic-$C$ monodomain of $\mathrm{d}\mathrm{i}-(4-n-\mathrm{d}\mathrm{e}\mathrm{c}\mathrm{y}\mathrm{l}\mathrm{o}\mathrm{x}\mathrm{y}\mathrm{b}\mathrm{e}\mathrm{n}\mathrm{z}\mathrm{a}\mathrm{l})-2-\mathrm{c}\mathrm{h}\mathrm{l}\mathrm{o}\mathrm{r}\mathrm{o}-1-4-\mathrm{p}\mathrm{h}\mathrm{e}\mathrm{n}\mathrm{y}\mathrm{l}\mathrm{e}\mathrm{n}\mathrm{e}\mathrm{d}\mathrm{i}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{n}\mathrm{e}$. The signal is attributed to thermally excited relative rotations of smectic layers as proposed by de Gennes. We discuss the anisotropy of the elastic and viscosity coefficients involved in this mode, by comparison with the nematic situation.

The theory of the three-wave parametric instability for weakly inhomogeneous media is derived with an application to laser pellet irradiation.

High-power pulse generators have been used to produce dense plasmas by the explosion of thin polymer fibers. Sufficiently high in energies have been achieved to produce large neutron yields. Neutron production is attributed mainly to the reaction $d(d,n)\mathrm{}{}_{}{}^3{}_{}{}^{}\mathrm{He}$ and neutrons are observed when either fibers containing the natural abundance of deuterium or nearly fully deuterated fibers are used. Results are given which show the variation of the neutron yield with initial fiber diameter and with deuterium content.

Experimental and theoretical evidence is presented to substantiate the collisionless nature of the interaction reported previously. We refute arguments claiming that the observed phenomena were collisional.

A computer was used to simulate ion acoustic wave generation by a grid. The self-consistent grid sheath and nonlinear effects were included. The experimentally observed wave propagation and Landau damping were reproduced quantitatively. Turning off the self-consistent electric field far from the grid left the "streaming" nature of the distribution function, the structure of the waves, and the magnitude of the damping essentially unchanged.

A small region of a magnetically confined, fully ionized arc plasma of density 2 × ${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$ and electron temperature of 1.3 to 1.7 eV is heated by 0.7 eV with pulsed C${\mathrm{O}}_2$-laser energy. The measured thermal decay is accounted for by classical collisional diffusion along the magnetic field.

If two laser beams have a difference frequency nearly equal to the plasma frequency, nonlinear interaction resonantly excites longitudinal plasma oscillations. These then induce transitions to other transverse modes. Nonlinear damping of the longitudinal mode heats the plasma. The process is optimized by having parallel beams, equal laser intensities, and damping equal to the frequency mismatch.

An investigation is made of the effect of order-parameter fluctuations on the nuclear relaxation time of superconducting $A15\mathrm{}$ compounds. It is found that because of the one-dimensional chain structure of these compounds the fluctuations make an important contribution to the NMR.

An effect analogous to the fountain effect in superfluid helium has been observed in a superconductor for the first time. A temperature gradient across a Pb-Pb point-contact junction produced a small supercurrent, which was detected by measuring the asymmetry of the critical current.

The scaling equation of state of an Ising-like ferromagnet is derived by an expansion in $\epsilon =4-d$, where $d$ is the dimension of space. The result is compared with numerical calculations on the three-dimensional Ising model. It is also established that the "linear model" is exact up to order ${\epsilon }^2$.

Experimental evidence is presented for radiative recombination of conduction electrons with hydrogenic impurity states in $n-\mathrm{I}\mathrm{n}\mathrm{S}\mathrm{b}$ between 2 and 4.2 K and magnetic fields up to 8 kG. The measured emission spectra agree with calculations by Larsen. In addition, radiative transitions between Landau levels are observed.