A high-gain, single-mode He-Ne 3.39-μm laser shows extreme mode pulling, as the laser operating frequency varies up to three times more slowly than the corresponding variation of the empty-cavity frequency. When the laser is operated at low pressures, new features appear in the vicinity of, and in conjunction with, the Lamb dip. Dispersive effects from the overlapping of the holes distorts the more nearly linear mode pulling observed for high pressures near line center. When the dispersive effects are strong enough instabilities are observed including self-pulsing, quasiperiodic, and chaotic output. At sufficiently high gain, the dispersion is distorted to give a multivalued region for the laser operating frequency for a single cavity frequency as predicted by Bennett.

Multiphoton interaction in free-electron lasers is studied using the correspondence principle. The developed theory is applicable to both quantum-mechanical and classical regimes of operation of the laser. The suggested formalism simplifies the traditional calculation of the small-signal, single-particle gain in the system. As an example, the theory is applied to the case of the free-electron laser operating in combined transverse helical and axial guide magnetic fields.

The decay of metastable states of a system obeying an $n$-variable Fokker-Planck equation is considered by evaluating the mean first-passage time $T_p$ using the asymptotic method of Schuss and Matkowsky. The statistics of the first-passage time $\tau$ in the small-noise high-barrier limit is shown to follow $〈{\tau }^r〉\simeq r!{〈\tau 〉}^r$, where $T_p=〈\tau 〉$, independent of the number of degrees of freedom, $n$. The time $T_p$ in the low-barrier, high-noise limit is also calculated. The hysteresis window for the control-parameter sweep rate is generalized to multivariate systems. These general results are applied to a model of a two-mode laser, where $n=4\mathrm{}$. A comparison with recent results of Mandel and co-workers is made, and experimental tests of the predictions are suggested.

The direct loss of fusion plasma energy via electrostatic plasma waves propagating across field lines has previously been shown to be significant. We investigate the theoretical foundations of this phenomenon from a strictly transport perspective. The critical role assumed by the displacement current in sustaining cross-field transport of electrostatic energy is shown. An accompanying analysis of the composition of electrostatic-wave-energy flux reveals a far larger involvement of the field degrees of freedom than that associated with wave-energy density. A phenomenological Fourier-type law describing wave-energy-current degradation by general wave-particle interactions is shown to be the appropriate description of wave-energy conduction in the nonthermal regime.

We report the first molecular-dynamic calculation of the quantum corrections of the pair-distribution function for a Lennard-Jones fluid. The method is based on the Wigner-Kirkwood expansion and is useful for "almost classical" many-body systems.

We introduce a class of models for the motion of a boundary between time-dependent phase domains in which the interface itself satisfies an equation of motion. The intended application is to systems for which competing stabilizing and destabilizing forces act on the phase boundary to produce irregular or patterned structures, such as those which occur in solidification. We discuss the kinematics of moving interfaces in two or more dimensions in terms of their intrinsic geometric properties. We formulate local equations of motion as tractable simplifications of the complex nonlocal dynamics that govern moving-interface problems. Special solutions for dendritic crystal growth and their stability are analyzed in some detail.

We present measured wavelengths of newly identified magnetic dipole transitions in the Mg I through Cl I sequences in zinc, germanium, and selenium that were excited after these elements were injected into tokamak plasmas in Doublet-III.

A single brief current pulse delivered to a spontaneously beating aggregate of cardiac cells from embryonic chick heart will reset the rhythm of the aggregate. The resetting depends on both the magnitude of the stimulus and the phase in the cycle at which the stimulus is delivered. Experimental data on resetting are fitted to an analytic function. This function, in turn, is used to construct a first return or Poincaré map which can be iterated to predict the effects of periodic pulsatile stimulation for any particular combination of frequency and amplitude of the stimulation. As the stimulation strength is increased the Poincaré map changes from a monotonic circle map of degree 1 to a nonmonotonic circle map of degree 1. The bifurcations in the frequency-amplitude parameter space are determined numerically by iterating the Poincaré map, and are compared with bifurcations in a simple model map and with those experimentally observed. These systems display period-doubling, intermittent, and quasiperiodic dynamics. Universal features of the bifurcations in the frequency-amplitude parameter space are described.

Anomalous relative diffusion (pair separation) in the inertial, as well as in the viscous, subranges of fully developed turbulent flow is considered. Using the Lagrangian velocity-correlation function in lowest-order continued-fraction approximation based on the Navier-Stokes equations and a phenomenological closure assumption, we express the variance in terms of the static structure function. This closed form for the turbulent diffusivity unifies scaling concepts with fluid mechanics and is free of fitting parameters. We obtain the following conclusions: Various regimes of variance versus time $t$ are identified, $\propto t^2$ initially, $t^1$ and exponential (viscous subrange), $t^{3+\gamma }$ (inertial subrange). Intermittency (well known to alter the scaling exponent) implies a fairly strong effect upon the magnitude of the diffusion depending on the intial separation and on the Reynolds number; diffusion is delayed with increasing intermittency. Incompressibility is expected to lead to differences in transverse versus parallel separation. Molecular diffusivity may show up even in the universal regime as a permanent enhancement of diffusion due to different incubation times.

The theory of spectral lines in a plasma with quasistatic ions is reconsidered. The ion microfield distribution, generalized to include field gradients and higher-order derivatives, is introduced without decoupling the ion and electron subsystems. It is shown that in a self-consistent treatment of ion-electron correlations the calculations of line shifts requires a more complete theory than has been used in the past. It is shown that level shifts due to a time average of the radiator-plasma interaction are closely related to shifts due to ion field inhomogeneities at the radiator. These two shifting mechanisms are not independent and the analysis indicates how to avoid overcounting. As a result, the time average of the radiator-plasma interaction, usually associated with the so-called plasma polarization shift, is formally different from the equivalent expression given by theories which treat electron-ion correlations in an ad hoc fashion.

High-resolution heat-capacity measurements have been carried out on the chiral and racemic versions of 2-methylbutyl-4′-$n$-pentyloxy-biphenyl-4-carboxylate (2M45OBC). Both smectic-$A$—smectic-$C$ and smectic-$A$—chiral-smectic-$C$ transitions are found to be mean-field-like with a large sixth-order term in the Landau free-energy expansion. Our results also shed light on similarities and differences between the chiral and racemic compounds.

The production of fast electrons in a keV plasma by both the two-plasmon decay and the stimulated-Raman-scattering instabilities is investigated. Two-plasmon-decay waves initially of 1.8 laser wave numbers are shown to trap electrons and subsequently heat them to energies exceeding the phase energy by a factor of 5 while stimulated-Raman-scattered electrons are observed at the phase energy of the absolute instability. Both instabilities are terminated by profile modification but can heat more than 1% of all the electrons in the focal volume.

We examine the onset of bound (i.e., localized) states in a high-temperature plasma consisting of electrons and ions. The onset of localization or ionization is related to the Mott and Anderson transitions of condensed-matter physics and to the breakdown of the Saha equation. We consider several models and develop a physically reasonable model of a plasma based on density-functional theory (DFT) where the mean ionic charge $\bar{Z}$ interpolates from the fully ionized limit to the atomic limit. This DFT model provides structure factors and Kohn-Sham eigenstates which are then used to calculate the self-energy of the one-electron Green function, thus transcending the local-density approximation and the well-known limitations of DFT, especially with regard to the excitation spectrum. The self-energy contains contributions from electron-electron and electron-ion density fluctuation effects, screening effects, and the renormalization of the propagators. The calculation yields shifted energy levels, widths, and level populations. The level widths are shown to be closely related to the electrical conductivity of Ziman-type formulations. The one-particle formalism used makes contact with the multiple-scattering theories of disordered materials, liquid metals, etc., and is a necessary first step to a future calculation of two-particle propagators and related properties.

A high-pressure shock wave generated by an underground nuclear explosion was used to obtain precise Hugoniot data from impedance-matching measurements at pressures ranging from 1 to 6 TPa and corresponding to threefold compressions. The shock passed from a 180-mm-diam by 17.5-mm-thick lead driver into a 12-mm-thick molybdenum base plate and then into a central 12-mm-thick ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ sample surrounded by stacks of the following pairs of 10-mm-thick samples (lower sample first): Mo-Pu ($\delta$ phase), W-Pb, A1-porous Mo (19% porosity), C-LiH, Cu-Au, and Fequartz (crystalline). Shock-front arrival-time measurements with 80 electrical-contact pins embedded in the assembly were used to determine shock velocities with uncertainties of 1.4-2.6%; the shock front was found to be slightly curved (with a radius of curvature of ∼2 m) but symmetric about the axis of the cylindrical driver with an upper limit on tilt asymmetry of 1.5 mrad. The measured shock velocity of 30.60 km/s in the molybdenum base plate corresponds to a pressure of 6.43 TPa based on the improved sesame equation of state (EOS) for molybdenum. Impedancematching analysis using the molybdenum base plate as the standard or reference material for the lower samples and using the lower samples as standards for the upper materials gave the following Hugoniot points in pressure ($P$) particle-velocity ($u$) coordinates for the indicated sample materials: A1($P=2.93\mathrm{}$ TPa, $u=27.57\mathrm{}$ km/s), porous Mo(4.65, 19.99), C(2.64, 28.38), LiH(1.225, 35.52), Cu(6.06, 21.15), Fe(5.71, 21.73), and quartz(2.75, 26.76). For the porous molybdenum sample, the calculated Hugoniot based on the sesame EOS barely lies within the region of uncertainty around the measured point. For the other samples, the calculated Hugoniots are in good agreement with the measured points.

The transfer of electronic energy by diffusion and by the dipole-dipole interaction in solids and liquids is modeled by a diffusion equation with an $r^{-6\mathrm{}}$ sink term plus a boundary condition at the distance of closest approach. The boundary condition is either absorptive, giving rise to diffusive transfer, or reflective, in which case the transfer is direct but modulated by diffusion. We solve the equation by a perturbation expansion in which the expansion parameter is inverse time, i.e., the $t\to \infty$ limit (the steady-state value) is reproduced exactly. The perturbation method gives accurate results for physically relevant values of the characteristic parameters and simple closed-form expressions for the time-dependent rate coefficient and the survival probability of an isolated pair are obtained for the first time when the diffusional transfer is larger than the direct transfer.

Computer experiments performed on a one-dimensional self-gravitating system are discussed from a dynamical and a statistical point of view. Statistically, the time-averaged position and velocity densities are shown to approach their respective microcanonical ensemble averages for four, five, and six particles. The relaxation time is much longer than previously expected. For three particles the system does not relax to the microcanonical distribution. We have explored the surface of sections for the $N=3\mathrm{}$ case and have correlated the statistical properties with explicit dynamical features. We show that this dynamical method is consistent with the statistical interpretation. The mechanism which generates the chaotic behavior for the $N=3\mathrm{}$ case is multiple encounters.

A general approach, within the framework of canonical quantization, is described for analyzing the quantum behavior of complicated electronic circuits. This approach is capable of dealing with electrical networks having nonlinear or dissipative elements. The techniques are applied to circuits capable of generating squeezed-state or two-photon coherent-state signals. Circuits capable of performing back-action-evading electrical measurements are also discussed.

We reconsider the problem of the adiabatic elimination of selected dynamical variables in the description of nonlinear systems, with a special emphasis on the identification of suitable criteria for the global validity of this procedure. The problem is analyzed in detail using as a guideline the one-mode homogeneously broadened laser model, with an injected signal and an arbitrary population difference for added flexibility. We propose five conditions for the global validity of the adiabatic limit, after consideration not only of the relative size of the time scales involved, but also of the magnitude of all parameters, of the physical variables, and of their fluctuations. The adiabatic elimination is formulated in the context of the dressed-mode description, leading to a generalization of the procedure adopted in earlier studies of multimode absorptive bistability. In addition, we establish a rigorous link between the adiabatic-elimination procedure and the multiple-time-scale approach to dynamic systems. The scaling behavior of the variables, of the eigenvalues of the linearized equations, and of the dressed-mode amplitudes and eigenvectors with respect to the smallness parameter of the problem is studied in detail. The relevance of what we shall define as "normal" and "anomalous" scaling in the text to the applicability of the adiabatic-elimination process is clarified. We also develop an alternative adiabatic-elimination scheme for the special case where all the rate constants of the system have the same order of magnitude, but another smallness parameter can be identified. From our analysis, it should be clear that our main conclusions are model independent, and not at all restricted to the specific features of the dynamical system selected as a test case for our discussion.

The static structure factor for colloidal suspensions in systems undergoing steady shear flow is calculated using response theory in the linear regime and using a fluctuating-diffusion equation in the nonlinear regime. In the second case, the intermediate-scattering function is also obtained. The theories give the structure factor for both high and low wave vectors. In the linear regime, both methods agree, although in certain wave-vector regions, the nonlinear terms cannot be ignored. When the theory is compared to that proposed using the "Stokes" assumption, some qualitative disagreements are found. The results are discussed in light of the experiments of Clark and Ackerson [Phys. Rev. Lett. 44, 1005 (1980)] and a possible experiment for determining the intermediate-scattering function is discussed.

A recent experiment indicates that clouds in the atmosphere have fractal surfaces which are characterized by a fractal dimension $D\sim 2.35$. Here we present a theory of the fractal dimension of clouds. We show that the fractal dimension of clouds is calculable from the theory of relative turbulent diffusion. We claim that previous approaches to the theory of relative diffusion are in contradiction with this experiment and that a newly developed theory gives $D\sim 2.35$ as a natural consequence. The new theory of relative diffusion is simultaneously in agreement with the intermittency-modified "$\frac{4}{3}$ (power) law" [i.e., the $\frac{(4+2\mathrm{}\mu )}{3}$ (power) law, where $\mu$ is the intermittency exponent].