A bandwidth-limited 30-psec laser pulse at 1.06 μm is used to investigate multiphoton ionization of noble gases at very high laser intensity (${10}^{15}$ W/${\mathrm{cm}}^2$). For helium atoms interacting with a laser intensity of 1. 1×${10}^{15}$ W/${\mathrm{cm}}^2$, no departure from a pure 22-photon ionization process is observed, in contradiction with the few theoretical calculations which predict that a tunneling effect should appear in this laser-intensity range.

The effect of photon correlations (coherence) on the transition probability of resonant two-photon processes is discussed. It is shown that coherence influences not only the transition probability but also the linewidth of the resonance. The implications for higher-order multiphoton ionization are discussed.

The one-dimensional electronic delocalization that results from the solid-state polymerization of diacetylenes produces a dramatic enhancement of the optical nonlinearities of these compounds. The third-order susceptibilities of the polymerized crystals reach very high values comparable to those of inorganic semiconductors.

Coherence phenomena such as photon echoes, free induction, and nutation effects are easily detected in molecular iodine using a frequency-switched tunable cw dye laser. This technique is generally applicable to atoms, molecules, and solids and offers unique ways for probing dynamic interactions in a selective manner. Elastic and inelastic collision mechanisms for ${\mathrm{I}}_2$ are examined independently and compared with theory.

Observations of stimulated Brillouin scattering from an underdense plasma in a magnetic field are reported. The shifts observed correspond with those expected from a plasma with the measured temperature. Scattering with twice the Brillouin shift $\delta \omega \simeq 2\delta {\omega }_A\simeq 4k_0{c}_s$ was observed when the fundamental Brillouin reflectivity approached 5%.

I present a new class of exact solutions for strong transverse electromagnetic waves in a cold overdense plasma, which incorporates both the exact traveling-wave and standing-wave solutions. The waves are circularly polarized, and the dielectric constant of the plasma is a function of $z$.

A set of equations describing the coupling of high-frequency electrostatic waves with ion fluctuations is obtained taking into account a nonisothermal state for the electrons. Stationary envelope solitons are found with narrow widths, slow velocities, and strong field intensities. For their existence the field intensity has to exceed a threshold which is determined by the number of reflected electrons.

The low-frequency stability of a field-reversed ion ring/layer of large Larmor radius in a background plasma is treated by a generalized form of the "energy principle."

A steep dip in the nuclear-spin-lattice relaxation time, $T_1$, of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in contact with CuTA [copper tetrammine sulfate monohydrate, Cu${\left(\mathrm{N}{\mathrm{H}}_3\right)}_4$S${\mathrm{O}}_4$·${\mathrm{H}}_2$O] has been observed near the ordering temperature, $T_{\mathrm{N}}=0.43\mathrm{}$ K, of CuTA. Data show that the electron-spin fluctuation in CuTA plays an important role for the relaxation mechanism of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ through the boundary interaction. An effective way of liquid-${}_{}{}^3{}_{}{}^{}\mathrm{He}$ cooling through this type of interaction is suggested.

An order parameter theory is derived and used to explain the observed structural phase transformations in tetrathiafulvalene tetracyanoquinodimethane. It is shown that there should be three transitions. One set of chains orders at 54 K, the other at 47 K. The modulation wave vector in the ${\overrightarrow{a}}^{*}$ direction is equal to $\frac{a^{*}}{2}$ between 54 and 47 K, increases as $\frac{a^{*}}{2}+\lambda {\mathrm{}(47-T)\mathrm{}}^{\frac{1}{2}}$ between 47 and 38 K, and locks to a value of $\frac{a^{*}}{4}$ below 38 K as a consequence of Umklapp terms in the free energy.

We measured the temperature dependence of the current and spin polarization, and determined the work functions from Fowler-Nordheim plots. The current increases exponentially with decreasing temperature. Work-function data can be related directly to the height of the internal W-EuS barrier. This barrier is lowered by magnetic splitting of the EuS conduction band for one electron-spin state which should lead to a spin polarization of unity. The measured spin polarization, however, is equal to the polarization of the $4f^7$ electrons of europium.

It is argued that a black hole can remain in thermal equilibrium with a heat bath even in the presence of particle interactions. This is achieved by proving the identity of the Hartle-Hawking Feynman propagator and a certain thermal Green's function.

The past and present observable properties of the Sun have been theoretically calculated on the assumption that the gravitational constant $G$ increases or decreases with time. Consideration of Davis's experimental upper limit on the present solar neutrino flux and of terrestial paleontological data sets a limit on the absolute rate of change of $G$, namely, $\left|\frac{{\dot{G}}_0}{G_0}\right|<\mathrm{}1\mathrm{}\times {10}^{-10\mathrm{}}/\mathrm{yr}$, if other standard constants do not also change with time.

The prolongation structure of Wahlquist and Estabrook is interpreted as a connection. In this way, some geometric insight might be provided for the description of those nonlinear partial differential equations which admit soliton solutions. A new geometric property—linked to the existence of an $\mathrm{SL}(2, R)$ connection—is proved for the solutions of the Korteweg-de Vries equation.

The velocities of neutrinos and muons originating from ${\pi }^{+}$ and $K^{+}$ decays have been compared using the California Institute of Technology-Fermilab detector in a narrow-band neutrino beam. A time-of-flight comparison between positive muons and neutrinos, as indicated by the final-state negative muons in neutrino interactions, yields $|{\beta }_{\nu }-{\beta }_{\mu }|<~0.4\times {10}^{-3\mathrm{}}$ (99% confidence level). We assume that $|1-{\beta }_{\mu }|<\mathrm{}{10}^{-5\mathrm{}}$ for these muons.

The interstellar magnetic field limits the monopole flux to < ${10}^{-16\mathrm{}}$ pole ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ and gives the average monopole energy ${10}^{11}$ GeV. They can be detected nonrelativistically only if their mass is ≳ ${10}^{11}$ GeV/${\mathit{c}}^2$ and, being produced at $E>\mathrm{}{10}^{22}$ GeV, require ${10}^{21}$ g ${\mathrm{cm}}^{-2\mathrm{}}$ matter for ionization loss to make them nonrelativistic. Massive monopoles can only be primordial or cosmologically produced. Low-mass monopoles trapped in dust grains and released in the atmosphere are possible.

We have performed microscopic calculations of the low-lying and high-lying $K^{\pi }=0^{+}, 1^{+}, \mathrm{and} 2^{+}$ states in deformed rare-earth nuclei. The centroids of the isoscalar giant quadrupole resonance in ${}_{}{}^{160}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$, and ${}_{}{}^{184}{}_{}{}^{}\mathrm{W}$ are at 11.58, 11.44, and 11.22 MeV, respectively. A broadening of these resonances due to the deformation is predicted which varies appreciably in the different nuclei. About 20% of the monopole strength is found in the same energy range.

The analog reactions ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$)${}_{}{}^{19}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$)${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ at 100 MeV have been utilized to study high-excitation, three-nucleon-cluster states in ${}_{}{}^{19}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$. Deformed-model calculations have been made in order to predict the energies of such high-lying states in terms of rotational bands with one or more particles in the $\mathrm{fp}$ shell. These show that the high-lying levels seen in the data can be explained by ${\mathrm{}\left(\mathrm{sd}\right)\mathrm{}}^2$ ${\mathrm{}\left(\mathrm{fp}\right)\mathrm{}}^1$ and ${\mathrm{}\left(\mathrm{fp}\right)\mathrm{}}^3$ configurations outside an ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ core.

The reaction ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ + ${}_{}{}^{50}{}_{}{}^{}\mathrm{Ti}$ is studied at 140-MeV laboratory energy. By means of a multi-parameter coincidence experiment in which two particles are detected and identified, the existence of a fissionlike binary mass division of a composite system with mass $A\approx 80$ is proved. The reaction is accompanied by the evaporation of about three nucleons.

Calculations for a single-$j$ nucleon coupled to an axially symmetric core with both ${\beta }_2$ and ${\beta }_4$ deformation have been performed for ${}_{}{}^{187}{}_{}{}^{}\mathrm{Ir}$. Using ${\beta }_4=-0.08\mathrm{}$, consistent with previously measured and predicted values of ${\beta }_4$, the calculated spectrum is competitive with recent calculations assuming an asymmetric core.