If an atom with a pair of spin-orbit-split state is coupled to two collinear fields, with one field resonant with the spin-orbit transition while the other is at a much lower frequency, then multiple Raman processes induce an electric dipole moment between the spin-orbit states; the spectrum exhibits the dynamic Zeeman effect; and there are interferences between the magnetic and field-induced electric dipole transitions.

Ramsey fringes have been observed using a stimulated, resonance Raman transition at 1772 MHz excited by two dye lasers in a sodium atomic beam. The width of the central fringe is 650 Hz (half width at half maximum), corresponding to a 30-cm interaction-region separation. The fringes are free from laser jitter because the jitters in both laser beams are correlated. Applications to frequency standards as well as to high-resolution spectroscopy in the microwave to far-ir regions are discussed.

Optical resonances with subnatural linewidth as narrow as 2.6 MHz have been observed with excellent signal-to-noise ratio in the Na $D_1$ line (natural width 10 MHz) in a polarization spectroscopy experiment. The new, subnatural resonances arise from Zeeman coherences which are produced by a strong probe beam and destroyed by a velocity-selective optical Hanle effect.

When laser light containing two frequencies ${\omega }_1$ and ${\omega }_2$ impinges on a plasma with ${\omega }_p={\omega }_1-{\omega }_2$ plasma waves are resonantly excited. The ponderomotive force of these waves is much larger than that of the beam, and the self-focusing effect is greatly enhanced. With use of C${\mathrm{O}}_2$ laser light of only 5 × ${10}^9$ W/${\mathrm{cm}}^2$ intensity and a plasma at 0.6% of critical density $n_c$, this effect is observed as a strong (${10}^5$-fold) enhancement of refracted light at $\theta =5\mathrm{}°-12\mathrm{}°$ when the density is at the resonant value.

The behavior of the specific heat of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, over a wide range of temperature, indicates a wiggle in the single-(quasi) particle spectrum $e\mathrm{}\left(k\right)\mathrm{}$ at $k_{\mathrm{F}}$. This wiggle corresponds to the enhancement of the effective mass $m^{*}\mathrm{}\left(k\right)\mathrm{}$ at $k_{\mathrm{F}}$ of current interest in nuclear physics. It can be quantitatively understood from the microscopic Hamiltonian within correlated-basis perturbation theory.

With use of low-energy electrons (40-400 eV) to scan single crystals of aluminum, diffraction patterns were discovered in the specimen-current images. The patterns have the symmetry of the reciprocal lattice and appear to be related to peaks in the curves of low-energy electron-diffraction intensity versus incident angle for a specified primary beam energy. These patterns provide a means to investigate surface phenomena.

The electronic structure of doped semiconductors is studied by using the best approximation of Klauder's impurity-scattering theory which yields a wave-vector- and energy-dependent self-energy $\Sigma (\overrightarrow{\mathrm{k}},E)$. An approximation is used for electron correlation effects. It is shown that as the impurity concentration is decreased, the conduction-band tail progressively splits off, giving an impurity band. The link between the formation of the latter and the general theory of bifurcation is outlined.

Time-differential perturbed angular correlation measurements of the nuclear quadrupole interaction of ${}_{}{}^{199m}{}_{}{}^{}\mathrm{Hg}$ labels introduced into the disulfide bridge of the activation domain of bovine trypsinogen reveal intramolecular reorientational motion over a wide angular range with a correlation time ${\tau }_c={11}_{-3\mathrm{}}^{+6\mathrm{}}$ nsec. No dynamics in this time range was observed in the trypsinlike complex formed with pancreatic trypsin inhibitor, where the activation domain is rigid.

Results of a numerical simulation of large-scale, plane, symmetric gravitational clustering of massive neutrinos are presented. It is shown that neutrinos may cluster in galactic halos in the adiabatic scenario of galaxy formation. The population of test particles exhibits very little phase mixing, suggesting that the scale of galactic halos may be set by the neutrino mass.

It is shown that the directed percolation on certain two-dimensional lattices, in which the occupation probability is unity along one spatial direction, is related to a random-walk problem, and is therefore exactly solvable. As an example, the case of the triangular lattice is solved. It is also shown that the square-lattice solution obtained previously by Domany and Kinzel can be derived using Minkowski's "taxicab geometry."

An exact vacuum solution of Einstein's field equations is presented, describing two isolated bodies balanced by their gravitational spin-spin interaction.

The analyzing power $A$ and spin-transfer parameters $K_{\mathrm{NN}}$, $K_{\mathrm{SS}}$, $K_{\mathrm{SL}}$, and $K_{\mathrm{LL}}$ have been measured in the $\mathrm{np}$ charge-exchange ($\mathrm{np}\to \mathrm{pn}$) region at 790 MeV. These data provide new and unique information on the spin dependence of the $\mathrm{np}$ interaction in the charge-exchange region. Models which explain the charge-exchange peak in the $\mathrm{np}$ elastic differential cross section as being due to interference between one-pion exchange and a slowly varying background are in basic agreement with the data.

A search for production of ${D^{*}}^{-}\text{'}\mathrm{s}$ using the decay chain $D^0{\pi }^{-}$, $D^0\to K^{+}{\pi }^{-}$, was carried out at the Brookhaven National Laboratory multiparticle spectrometer with a 16-GeV/c ${\pi }^{-}$ beam and a hydrogen target. At 95% confidence level the upper limits for the product of peripheral production cross section by branching ratio are 2.4 nb for inclusive ${D^{*}}^{-}$ production and 1.3 nb for the exclusive channel ${\pi }^{-}p\to {D^{*}}^{-}{\Lambda }_c$.

The angular distribution of the continuum in the reaction ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}(p, p^{\prime }){}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$ at $E_p=800\mathrm{}$ MeV shows a marked decrease in cross section toward small scattering angles (${\theta }_L<6\mathrm{}°$). This behavior is well described by a single scattering model which includes the effects of Pauli blocking. Continuum analyzing power data are found to be very close to the values for free $p-p$ and $n-p$ scattering. However, spin-flip probabilities in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ ($E_p=400\mathrm{}$ MeV) and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ ($E_p=500\mathrm{}$ MeV) are significantly smaller than the free nucleon values.

The radiative lifetime of metastable ${\mathrm{N}}^{+}\left({}_{}{}^5{}_{}{}^{}S_2^{}{}_{}{}^{}\right)$ has been measured to be 4.2±0.6 msec, a value generally in agreement with theory, by direct monitoring of the spontaneous emission from ∼ 1$0^6$ ${\mathrm{N}}^{+}$ ions stored in a radio-frequency ion trap. Additional measurements were made of the quenching rate coefficient (2.5×${10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$) and the production cross section (≥ ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$) of ${\mathrm{N}}^{+}\left({}_{}{}^5{}_{}{}^{}S_2^{}{}_{}{}^{}\right)$ in ${\mathrm{N}}_2$. This work supports the interpretation of the 2145-Å feature in the spectrum of aurorae as being due to ${\mathrm{N}}^{+}\left({}_{}{}^5{}_{}{}^{}S_2^{}{}_{}{}^{}\right)$ emission.

The degenerate and counterpropagating waves of the degenerate four-wave mixing process will appear nondegenerate and noncounterpropagating to a moving observer. A Lorentz-transformed degenerate four-wave mixing is seen to be indistinguishable from coherent anti-Stokes Raman scattering. Inverse transformations which render any given coherent anti-Stokes Raman scattering the appearance of a degenerate four-wave mixing are also presented.

Collisionless plasmas imbedded in a magnetic field and with the electron temperature transverse to the magnetic field larger than the longitudinal temperature can be subject to an instability that produces transport of transverse electron thermal energy into the regions where the magnetic field is weakened by the perturbation while the plasma motion is decoupled from that of the magnetic field lines.

Studies of surface extended x-ray-absorption fine structure reveal unexpected adsorption site variations for I and Te adsorbed on Si and Ge surfaces. Iodine is found to occupy the atop site on both Si{111} 7×7 and Ge{111} 2×8 whereas Te occupies two distinct and previously unreported bridging sites on these surfaces.

The Raman scattering spectrum of silica was measured to low temperature and very small frequency shifts. Strain-free cooling of a long silica-core fiber allowed us to investigate Raman scattering of the two-level tunneling systems to 1.5 K. A considerable central line broadening from relaxation of two-level tunneling systems is evident, although the predicted strong scattering contribution from resonant two-level tunneling centers at very low temperature and small frequency shift was not observed.

First-principles total-energy calculations by two independent methods predict new transition-metal-like sequences of stable crystal structures in the third-period simple metals Na, Mg, and Al, under increasing pressure. These structural phase transitions are controlled by $d$ electrons through the lowering and partial filling of the initially empty $3d$ band as the metals are compressed. A number of these transitions occur in the megabar range and below and could be investigated by existing experimental techniques.