Recently measured properties of the prescission particle emission from heavy-ion induced fission of systems with A∼200 were analyzed using the statistical model. Simultaneous fits to prescission neutron, proton, and α-particle multiplicities and mean kinetic energies can be obtained when the deformation dependence of both the particle transmission coefficients and particle binding energies are taken into account. The experimental data are consistent with a total fission time scale of (30±10)×${10}^{\mathrm{-}21}$ s, with more than half of this time being spent beyond the saddle point.

Quantization of atomic motion is observed in two- and three-dimensional cesium optical molasses by stimulated Raman spectroscopy. A new geometry is used with the minimum number of laser beams, so that the topography of the optical potential is not sensitive to phase drifts of the molasses beams. The deepest potential wells are located on a hexagonal lattice in two dimensions and on a body-centered-cubic lattice in three dimensions. They correspond to purely circularly polarized light, allowing a Lamb-Dicke narrowing of the transitions between vibrational levels to occur.

A new magneto-optical trap is demonstrated which confines atoms predominantly in a ‘‘dark’’ hyperfine level, that does not interact with the trapping light. This leads to much higher atomic densities as repulsive forces between atoms due to rescattered radiation are reduced and trap loss due to excited-state collisions is diminished. In such a trap, more than ${10}^{10}$ sodium atoms have been confined to densities approaching ${10}^{12}$ atoms ${\mathrm{cm}}^{\mathrm{-}3}$.

We present the first experimental demonstration of optical cooling of atomic hydrogen. Two methods are discussed: Doppler cooling, for which we report a minimum achieved temperature of 8 mK, and light-induced evaporation, a new cooling method by which we reached 3 mK.

Using the extreme resolution of a cold hydrogen beam spectrometer and a novel sideband technique, the isotope shift of the 1S-2S transition of hydrogen and deuterium has been directly measured to an accuracy of 3.7×${10}^{\mathrm{-}8}$. Our experimental result of 670 994 337(22) kHz is compared with the theoretical prediction of 670 994 414(22) kHz that can be calculated, if we assume the value of 1.9627(38) fm for the structure radius of the deuteron and 0.0189(4) ${\mathrm{fm}}^2$ for the neutron-electron correction. The 2.5σ difference between the predicted and the measured values may be interpreted in terms of polarizability of the deuterium nucleus.

Orthopositronium (o-Ps) decay or conversion into ‘‘invisible’’ final states is searched for by measuring the energy deposited in a hermetic photon detector for each positron produced from ${\mathrm{\beta }}^{+}$ decay of ${}_{}{}^{22}{}_{}{}^{}\mathrm{Na}$ and stopped by an aerogel target. No invisible event is detected for a total of ${10}^8$ stopping positrons, thereby giving an upper limit of 2.8×${10}^{\mathrm{-}6}$ on the o-Ps branching ratio, which is 200 times more stringent than previous limits. This experiment excludes an invisible decay as the origin of the reported discrepancy on o-Ps lifetime, provides a limit of ε<1.5×${10}^{\mathrm{-}8}$ on the photon–mirror-photon mixing, and rules out millicharged particles lighter than 500 keV.

Quantum Langevin equations and a master equation are derived for a two-atom system in which the first atom is driven by coherent field, and the fluorescent light used to drive a second atom. We show that the light beams from both atoms are antibunched, and that they are mutually anticorrelated.

The quantum trajectory theory of an open quantum system driven by a photoemissive source is formulated. The formalism is illustrated by applying it to photon scattering from an atom driven by strongly focused coherent light.

By increasing the Fresnel number F of the cavity of a photorefractive oscillator, we report the transition from a boundary-controlled regime, where the size of the transverse patterns scales as 1/ √F , to a bulk-controlled regime where the pattern size is independent of F. In this new regime, the size corresponds to an intrinsic correlation length imposed by diffusion processes within the material. The wave number spectrum of the emitted field has a sharp cutoff, corresponding to the length scale of bulk correlations. Such a new behavior is explained by the wave number dependence of the gain within the instability region.

We report the first observation of a spectral resonance in the lateral displacement (Goos-Hänchen shift) of a laser beam totally reflected from a glass-cesium vapor interface. The line shape and the magnitude of the effect are well described by a model taking atom-wall collisions into account.

We propose a scheme for producing a spatial and temporal averaged gain of 45 ${\mathrm{cm}}^{\mathrm{-}1}$ in nickel-like Ta, including refraction. This result is achieved by irradiating a 40 μg/${\mathrm{cm}}^2$ target with a low intensity pulse [2ω(λ=0.53 μm), 5×${10}^{13}$ W/${\mathrm{cm}}^2$, 80 ps] to make the plasma subcritical. This is followed by a high intensity pulse (2ω, 2×${10}^{15}$, 20 ps) to give the proper ionization. Therefore the principle of pulse shaping to achieve high gain using high intensity pump radiation is demonstrated.

Periodic two-dimensional waves on the surface of a flowing film are generally unstable. We have investigated their breakdown experimentally to determine the process by which film flows undergo a transition to spatiotemporal chaos. The two-dimensional secondary instabilities studied here are convective (like the primary instability); both subharmonic and sideband instabilities occur, but in different ranges of frequency.

Atomic-scale compositional ordering in ${\mathrm{Si}}_{\mathit{x}}$${\mathrm{Ge}}_{1\mathrm{-}\mathit{x}}$ alloys is directly linked to the formation of coherent islands during Stranski-Krastanow growth. The vicinal surfaces associated with nonequilibrium island shapes induce a bilayer step flow growth mode, and the ordering results from Ge segregation at ${\mathit{D}}_{\mathit{B}}$ kinks.

The conformation of a main-chain liquid crystalline polyester in its oriented nematic phase has been determined by small-angle neutron scattering. The data are fitted by a model of rigid cylinder with orientational fluctuations. For a low degree of polymerization (∼9) the chain is almost completely elongated in the direction of the nematic field. For a polymer 3 times longer, the existence of two hairpins is shown at high temperature; this number decreases with decreasing temperature.

We have observed a two-vibron bound-to-unbound transition in solid ${\mathrm{D}}_2$ by Raman scattering at a pressure of 34(2) GPa. We investigated the transition by increasing the vibron bandwidth, through the application of presssure, until it dominated the intramolecular anharmonicity. We present an analysis of a simple Hamiltonian that gives the experimental bivibron binding energy and the critical bandwidth-to-anharmonicity ratio. Our results indicate that while the vibron bandwidth increases markedly with pressure, the anharmonicity remains constant.

The shapes of coherent misfitting ${\mathrm{Ni}}_3$Al precipitates were systematically investigated using a parameter ζ defined essentially by the ratio of particle sizes along 〈100〉 and 〈110〉. The variation of ζ with size was measured in several alloys using electron microscopy. ζ does not depend uniquely on particle size; it is also strongly influenced by the volume fraction of ${\mathrm{Ni}}_3$Al. These results provide the first quantitative evidence that elastic interaction energy plays a major role not only in spatial correlations, but also in the morphological evolution of individual particles.

A new branch of weakly damped collective magnetic excitations in spin-polarized low-density systems is predicted. This type of wave corresponds to the transverse oscillations of the macroscopic quadrupole moment while the magnetization does not oscillate. The spectra of both spin waves and quadrupole modes are calculated. The theory can be applied to gaseous H↓, D↓, and other rarefied gases of S=1 particles.

Using infrared-visible sum-frequency generation we have obtained the OH stretch vibrational spectra of water at the vapor/water interface. From the spectra, we deduce that more than 20% of the surface water molecules have one free OH projecting into the vapor. The spectrum is weakly temperature dependent from 10 to 80 °C. A monolayer of fatty alcohol on water surface terminates the free OH groups and induces an icelike structure in the spectrum.

Light-induced persistent change in the concentration of occupied shallow donors (photomemory effect) in ${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$${\mathrm{Te}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Se}}_{\mathit{y}}$:In has been used for determining the contribution of donor-bound magnetic polarons to the total magnetization of the crystal. This contribution must be taken into account in any precise description of low temperature properties of diluted magnetic semiconductors containing shallow donors. The observed agreement between experimental data and the theory of bound magnetic polarons provides additional support for the negative-U model of DX-like centers in II-VI semiconductors.

We report a systematic study of the low-temperature Hall resistance ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$ in the reentrant insulating phase (IP) around the 1/5 fractional quantum Hall (FQH) liquid. At filling factors ν=1/5 and ν=2/9, ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$=5h/${\mathit{e}}^2$ down to 22 mK and ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$=9h/2${\mathit{e}}^2$ down to 40 mK, respectively. In the reentrant IP for ν>1/5, and for ν<1/5 near the 1/5 FQH liquid, ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$ is normal (=B/ne) and independent of T. Our experimental findings directly imply that ${\mathrm{\sigma }}_{\mathit{x}\mathit{x}}$→0 and ${\mathrm{\sigma }}_{\mathit{x}\mathit{y}}$→0, but ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$→B/ne as T→0 in these IP regions. We discuss implications of the findings with regard to the various theoretically proposed ground states for the IP.