The width of the picosecond optical pulses produced in the Stanford University 3-μm free-electron laser has been measured by using optical autocorrelation techniques. The pulse width was measured as a function of cavity length detuning and compared with the laser linewidth. The optical pulses are nearly transform limited and somewhat shorter than expected at large values of the cavity length detuning.

The collective free-electron laser interaction has been studied at millimeter wavelengths using a newly designed experimental apparatus which features an electron beam of low emittance. Measurements in a superradiant amplifier configuration indicate the production of 35 MW at ∼4 mm with an efficiency of 2.5%. The parametric dependence of power thresholds and wavelength on pump and guide magnetic fields are shown to be in agreement with theory.

A new amplification mechanism for self-induced magnetic fields and the associated filamentation of hot-electron flow by these magnetic fields are demonstrated. The amplification mechanism is due to a spatially nonuniform convection and a consequent piling up of the magnetic field, related to hot-electron energy deposition. Two-dimensional simulations, showing the space-time evolution of magnetic field fluctuations, and a theoretical interpretation are provided.

A statistical theory for the properties of current-carrying plasma is postulated. The small-scale magnetic turbulences are isotropic in $\overrightarrow{\mathrm{k}}$ and have a wave-number spectrum similar to that of black-body radiation. The electron transport coefficient is found to have an $n^{-1\mathrm{}}$ dependence and a numerical value remarkably close to that of the empirical Alcator scaling. The frequency spectrum (as seen by a magnetic probe) is also calculated and is in good agreement with experimental results. Some unresolved questions are discussed.

The local character, in poloidal mode-number space, of the resonant nonlinear interaction of drift waves with ions in a sheared magnetic field permits an analytical determination of the spectrum. Important processes underlying the stabilization are energy cascade and transfer, respectively, in "close" (${k_{\theta }}^{\prime }\cong k_{\theta }$) and "distant" (${k_{\theta }}^{\prime }{a}_s\cong \frac{1}{k_{\theta }{a}_s}$) interactions. The spectral index $n=4\mathrm{}$ of the high-mode-number tail is independent of the excitation mechanism.

The effect of a nonuniform laser beam on the ablative acceleration of thin foils is investigated by using the fast2d laser-shell simulation code. The results show that laser nonuniformities with scale lengths greater than the distance from the ablation surface to the critical surface would have a severe impact on drive pressure symmetry and hence on pellet gain.

The x-ray spectrum emitted by a gas jet irradiated at ${10}^{16}$ W/${\mathrm{cm}}^2$ has been measured for laser wavelengths of 1.05 and 0.53 μm. The flux of hard x rays ($h\nu >~10$ keV) emitted by a gas jet is less than 0.3% of that emitted by a glass target irradiated at the same intensity. This low flux implies that less than 0.1% of the incident energy is used to heat electrons to energies greater than 10 keV.

The enhancement of diffusion perpendicular to a strong magnetic field, induced by low-amplitude field fluctuations, is calculated. A novel fluid representation of a model Fokker-Planck transport equation is used to show the equivalence of the above problem to that of a passive scalar advected by a prescribed fluctuating velocity field.

Exact periodic solutions are found for three-dimensional lattices with fourth-order on-site electron-ion potentials. Numerical results are presented for ferroelectric SnTe. The coupling of these nonlinear waves with phonons is investigated for phase transitions with finite critical wave vectors. For ${\mathrm{K}}_2$${\mathrm{SeO}}_4$ both the paraelectric-incommensurate and the incommensurate-commensurate ferroelectric transitions are analyzed. The cubic power of the nonlinear force leads to a lock-in transition at the wave vector $\frac{2\pi }{3}$.

The time-resolved optical transmission and reflectivity of $n$-type crystalline silicon has been observed during and after pulsed-laser irradiation. The transmission goes to zero, and remains at zero, during the period of enhanced reflectivity, contradicting reports of earlier experiments. Our measurements are in quantitative agreement with results of thermal melting model calculations and with known optical properties of molten silicon.

Experimental evidence is presented for radiative transitions of light holes accumulated in a limited area in momentum space to the heavy-hole band. Also reported is the observation of cyclotron resonance emission from the accumulated light holes. The possibility of far-infrared amplification is discussed.

Studies of the de Haas—van Alphen spectra arising from the two-dimensional lattice of magnetic-breakdown—coupled orbits in magnesium contain spectral features which disagree qualitatively with the accepted theory of Falicov and Stachowiak. Their theory, which was thought to be equivalent to Pippard's theory for the magnetic band structure, is shown to be inequivalent.

Bremsstrahlung isochromat spectra at $\hslash \omega \cong 9.7$ eV were recorded from well characterized, clean Pt(111), Pt(100)1×1, and Pt(210) surfaces. These spectra show intense emission peaks at the Fermi level as well as smaller peaks whose positions and intensities vary with the orientation of the substrate and the angular range of the incident electrons. The large peaks at the Fermi level are due to the high density of unoccupied $5d$ states. The orientation-dependent peaks are assigned to direct optical interband transitions between unoccupied states.

Ultraviolet isochromat spectra ($\hslash \omega =9.7\mathrm{}$ eV) have been taken on the single-crystal surfaces Cu(001) and Ni(001) as a function of the angle of incidence of the incoming electrons. The energy dispersion and intensity variation of the observed peaks in the isochromat spectra are interpreted successfully in terms of direct transitions within the bulk band structure.

It is shown that the laws of physics impose no fundamental bound on the rate at which information can be processed. Recent claims that quantum effects impose such bounds are discussed and shown to be erroneous.

By exploitation of the overcompleteness of coherent states expressions are presented for path integrals in terms of genuine (Wiener) path-space measures for driven harmonic oscillators which when projected onto the subspace spanned by coherent-state matrix elements yield the appropriate quantum mechanical propagator.

The universal Newtonian gravitational constant is being redetermined at the National Bureau of Standards with use of the method of Boyes in which the period of a torsion pendulum is altered by the presence of two 10.5-kg tungsten balls. The difference in the squares of the frequencies with and without the balls is proportional to $G$. The resulting value of $G$ is (6.6726±0.0005)×${10}^{-11\mathrm{}}$ ${\mathrm{m}}^3$· ${\sec }^{-2\mathrm{}}$· ${\mathrm{kg}}^{-1\mathrm{}}$·

A simple procedure is presented for extracting a new model-insensitive, inelastic strength factor $A_L$ for Tassie-like nuclear excitations directly from the data. $A_L$, a measure of the coupling strength at large momentum transfer, is to be contrasted with the low-momentum-transfer $B\left(\mathrm{EL}\right)\mathrm{}$. $A_L$ is extracted for the $3^{-}$ (2.61) and $5^{-}$ (3.2) states in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ and the $2^{+}$ (1.3) state in ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$, showing that these excitations are Tassie-like and that for the $3^{-}$ state $A_L$ is projectile independent.

The electron and antineutrino spectra from the products of thermal fission of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ were calculated. A microscopic calculation of the $\beta$-decay schemes of the neutron-rich fission products led to an accuracy in absolute and relative shapes of the predicted $e^{-}$ and $\overline{\nu }$ spectra of <5% in the range $2.5<~E<~7.5$ MeV. The calculations yield, together with the recently calculated $\overline{\nu }$ spectrum of the fission products of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, the first reliable theoretical basis for the interpretation of reactor antineutrino-oscillation experiments.

It is shown that, unlike in neutral Ba, the $4d\to 5f$ transitions cannot be neglected in the interpretation of the $4d$ spectrum of ${\mathrm{Ba}}^{++}$. A term-dependent hybridization of the $5f$ wave functions occurs, the effects of which reverse between Ba and ${\mathrm{Ba}}^{++}$, and oscillator strength reappears in the $4d\to \mathrm{nf}$ ($n>~5$) transitions. A second kind of wave-function collapse is identified and its effects are described.