The evolution of the polarization state of an intense laser wave in uniaxial nonabsorbing crystals is considered with use of analytical and numerical methods. It has been found that, depending on the initial conditions, the polarization ellipse rotates or oscillates, changing its shape and handedness. A detailed study of various cases is performed.

The inception of the cathode region of a transitory discharge in ${\mathrm{CO}}_2$ is studied by means of a spatio-temporal second-order hydrodynamic model (continuity equations for electrons and ions, momentum and energy equations for electrons). The electric field is calculated by Poisson equation. This first paper deals particularly with the formalism developed for this study. A term-to-term analysis of the equations allows the characterization of the physical mechanisms governing each part of the cathode region. The balance between the electric field acting as a source of energy and the elastic and inelastic collisions acting as loss processes is studied. The whole collective phenomena in the discharge (diffusion and work of electronic pressure strength which are made explicit by the gradients in the equations) play a regulating role in relation to the energy-gain or -loss processes. In a place where the field action is significant, i.e., in the cathode fall, they contribute to reduce this action and are energy- and velocity-loss processes for the electrons, whereas, in the negative glow, they compensate for the quasinull action of the electric field, and thus they are the only processes maintaining the energy and the velocity of the electrons in this zone. The cathode-fall–negative-glow transition zone is defined as the zone where the action of the energetic collective phenomena (total diffusion, work of electron pressure) is reversed.

The inception of the cathode region is described by a second-order hydrodynamic model proposed in the preceding paper. The spatio-temporal variations of ionic and electronic densities, electron temperature, electron pressure, and electric field are provided. The double nonequilibrium between the electrons and the electric field due to strong electric field gradients and to secondary emission at the cathode is carefully studied. The way these electrons emitted by the cathode join the discharge is studied as a function of their emission temperature. The evolution of the electron temperature shows a maximum shifted from the field maximum. This leads to a difference between the non- equilibrium apparent ionization coefficient (deduced from the dynamic temperature) and the corresponding equilibrium coefficient. The maximum drop of the electric field and almost the main part of the processes that sustain the discharge occur in the transition zone situated between the cathode fall and the negative glow. In this zone, the electron energy density (electron pressure) is maximum involving a maximum in the reaction rates (the ionization, excitation rates, and the electron current density are maximum). When the electron current density increases, the electric field at the cathode increases as the cathode-fall length decreases.

A field-theoretic approach, analogous to Kraichnan’s direct-interaction approximation, to the stability theory of complex three-dimensional flows is developed. The long-wavelength stability of a class of Beltrami flows in an unbounded, viscous fluid is considered. We examine two flows in detail, to illustrate the effects of strong isotropy versus strong anisotropy in the basic flow. The effect of the small-scale flow on the long-wavelength perturbations may be interpreted as an effective viscosity. Using diagrammatic techniques, we construct the first-order smoothing and direct-interaction approximations for the perturbation dynamics. It is argued that the effective viscosity for the isotropic flow is always positive, and approaches a value independent of the molecular viscosity in the high-Reynolds-number limit; this flow is thus stable to long-wavelength disturbances. The anisotropic flow has negative effective viscosity for some orientations of the disturbance, and is therefore unstable, when its Reynolds number exceeds √2 .

Nonlinear electromagnetic wave propagation is investigated in a system consisting of a relativistic, cold-electron beam propagating through a helical wiggler magnetic field. By transforming to wiggler coordinates and introducing the traveling-wave ansatz, a set of three, coupled, nonlinear ordinary differential equations is derived which describes nonlinear wave propagation in the system. In the Compton-regime limit, the number of differential equations reduces to two. These equations are particularly useful for studying nonlinear saturated states of the free-electron-laser instability, corresponding to values of the dimensionless phase speed (β=u/c) that are less than the dimensionless beam speed (${\beta }_b$=$V_0$/c).

The nonrelativistic Schrödinger equation is supposed to yield a pairwise $R^{\mathrm{-}6}$ attractive interaction among atoms or molecules for large separation, R. Up to now this attraction has been investigated only in perturbation theory or else by invoking various assumptions and approximations. We show rigorously that the attraction is at least as strong as $R^{\mathrm{-}6}$ for any shapes of the molecules, independent of other features such as statistics or sign of charge of the particles. More precisely, we prove that two neutral molecules can always be oriented such that the ground-state energy of the combined system is less than the sum of the ground-state energies of the isolated molecules by a term -${\mathrm{cR}}^{\mathrm{-}6}$ provided R is larger than the sum of the diameters of the molecules. When several molecules are present, a pairwise bound of this kind is derived. In short, we prove that in the quantum mechanics of Coulomb systems everything binds to everything else if the nuclear motion is neglected.

Using an electron beam (250 kV, 200 A, 900 ns maximum pulse length) to excite ultrapure helium at a pressure of 1000 Torr, we have observed previously unreported emissions near 431 nm. These intense emissions are molecular in nature (both Q and R branches are resolvable) and have very slow rise and decay times relative to the rise and fall times of the electron-beam current pulse. A rotational constant derived from those emissions indicates that they do not originate from something other than a helium molecular species.

A mechanism is proposed in which second-harmonic emission is generated due to the coalescence of two surface waves counterpropagating along the critical surface of a laser-produced plasma. The waves are resonantly excited by a laser beam focused upon the inhomogeneous plasma whose density profile is steepened in the vicinity of the critical density. The necessary condition for this mechanism to operate is, however, the presence of a dc magnetic field in the critical region.

Absorption spectroscopy has been used in this work to diagnose the conditions in the pusher of laser-imploded targets. Absorption lines are produced when continuum radiation from the hot central compressed gas passes out through the colder surrounding pusher. They can be used to determine both the temperature and the ρ ΔR product of the pusher around peak compression. Fair agreement is found between the experimental absorption spectra and simulations calculated by a hydrodynamic code. Applications of this work to the diagnosis of future, high-compression implosions is discussed.

An algorithm is presented for the detailed computation of the spectral lines in hot, partially ionized plasmas in local thermodynamic equilibrium. The procedure uses the wave functions and state probabilities determined from the average atom model for microscopic configuration accounting. We use intermediate coupling to include the detailed structure of the bound-bound transition arrays. The model is applied to bromine plasma under such temperature and density conditions that partially filled L shells occur.

The aim of this study is to show the influence of the repulsive part of the intermolecular potential on the thermodynamical properties of hot gases at high pressures. For this purpose, a new model of equation of state, based on intermolecular potentials, has been built for gases at high temperature throughout a large range of pressure (1 bar to 0.5 Mbar). Two equations of state, based on this model, are compared in order to show the influence of the repulsive exponent of the potential on the thermodynamic properties of detonation products. Calculated results are compared to experimental data.

Free-energy formulas applicable to the electron-screened ion plasmas are derived in the hypernetted-chain approximation. The formulas are expressed in terms of the correlation functions and do not involve cumbersome thermodynamic integrations. Accuracy and thermodynamic consistency of the proposed formulas are examined and ascertained through explicit numerical comparison with the results of other independent calculations taking account of electronic screening in the interionic potentials.

The stochastic evolution in space of an electron avalanche has been investigated with the use of Monte Carlo methods. From these investigations we have obtained the energy distribution as a function of distance from the cathode and avalanche size, f(n,ε,x); the probability distribution for avalanche size, P(n,x); and the ionization probability, per unit distance at x, for electrons belonging to an avalanche of size n, ${\alpha }_s$(n,x). We believe that this is the first time that any information has been presented on f(n,ε,x) and ${\alpha }_s$(n,x) which takes microscopic processes into account. The investigations were done in nitrogen for E/N≥300 Td. We suggest that pulse-height distribution experiments may be a sensitive technique for determining the E/N conditions at which runaway electrons appear.

We have measured the profiles of plasma-broadened, slightly red-shifted spectral lines of neutral argon with a wall-stabilized arc and performed a detailed line-shape analysis with a computerized data acquisition and processing system. According to Stark broadening theory, isolated lines of neutral atoms in dense plasmas are broadened mostly by electron impact, which results in symmetric Lorentzian profiles. An additional small broadening contribution, which is asymmetric in nature, is due to the plasma ions. This difference in symmetries provides the possibility of separating ion broadening effects from the electron broadening. In full agreement with the quasistatic theory of ion broadening, our experiment shows asymmetry patterns with characteristic minima and maxima near the central part of the lines. While the positions of these extrema—as well as the zero crossing point—stay essentially constant for all lines when compared on a reduced wavelength scale, the amplitudes of the extrema vary from line to line. Measurements of the amplitudes thus allow, by comparison with theoretical asymmetry patterns, the determination of ion broadening parameters.

We have obtained self-consistent solutions to the hypernetted-chain integral equation in a planar surface geometry. The surface density profiles are monotonic with a constant negative gradient and show no surface structure. We compute the surface total correlation function and direct correlation function and also report on the temperature dependence of the surface tension, the position of the Gibbs dividing surface, and the surface width.

Thermal fluctuations around inhomogeneous nonequilibrium steady states of one-dimensional rigid heat conductors are analyzed in the framework of generalized fluctuating hydrodynamics. The effect of an external source of noise is also considered. External fluctuations come from temperature and position fluctuations of the source. Contributions of each kind of noise to the temperature correlation function are computed and compared through the study of its asymptotic behavior.

The three-dimensional diffusion in condensed material of a rotating and translating asymmetric-top molecule is considered with use of three frames of reference: the laboratory frame (x,y,z), a rotating frame (1,2,3)’, and a moving frame (1,2,3). The frame (1,2,3)’ has the same origin as (x,y,z), but rotates with an angular velocity ω, the molecular angular velocity. The frame (1,2,3) is defined by the principal molecular moments of inertia, and its origin is therefore the molecular center of mass. The molecular angular velocity ω is the same in all three frames. By writing a pair of simultaneous single-molecule Langevin equations, a rotational equation in (1,2,3) and a translational equation in frame (1,2,3)’, a natural description of the molecular diffusion is obtained without the need of friction cross terms. This description introduces into the analysis the center-of-mass position vector r, and the forces obtained by transforming Newton’s equation into a noninertial frame, i.e., by the frame transformation (x,y,z)→(1,2,3)’ or vice versa.

These are the Coriolis force 2mω×v, the centripetal force mω×(ω×r), and the force mω̇×r. The analysis also implies the consideration of the velocity ω×r. Here v is the molecular center-of-mass linear velocity, ω the angular velocity, and r the position vector of the center of mass. It is shown by computer simulation that autocorrelation and cross-correlation functions of these terms can exist both in frame (x,y,z) and in frame (1,2,3), the moving frame. Examples are provided in the liquid state for the achiral asymmetric top dichloromethane and for the enantiomers and racemic mixture of bromochlorofluoromethane at two state points. The symmetry properties of some of the new cross-correlation functions are tabulated. Finally, experimental methods are suggested for observing cross-correlation functions such as these and for testing experimentally the detailed numerical paradigm provided by these computer simulations. Examples of one method are given with reference to the far-infrared power absorption of the tris(acetylacetonate) complexes of cobalt and chromium in the powdered crystalline state.

Ground-state energies as well as corresponding stability thresholds characterizing several theoretical or phenomenological potentials which are of interest in the description of quarkonia have been established and discussed. For this purpose a nonperturbative quasiclassical method for the evaluation of the ground-state energy proposed previously has been used. We are then led to establish ground-state energies for nonrelativistic as well as for relativistic spin-(1/2) particles. In this respect, Coulomb inverse-logarithmic potentials, linear plus Coulomb potentials, power potentials, and superpositions of power potentials have been considered. In addition, the ground-state energy characterizing the relativistic Dirac bag model has also been established and discussed.

A two-level system contained in a single-mode resonant cavity tuned to the energy-level separation of the two-level system is studied. A purely quantum-level description is converted into five coupled ordinary differential equations for certain relevant expectation values. These equations are identical with a system of equations proposed by Belobrov, Zaslavskii, and Tartakovskii on semiclassical grounds, and very closely related to a similar system proposed by Milonni, Ackerhalt, and Galbraith on semiclassical grounds. The level-population expectation value for the two-level system shows a transition to chaos as the coupling strength is increased. This transition is suggested by power spectra and confirmed by calculation of corresponding Liapunov exponents. It is shown that the equations can be transformed so that they exhibit the presence of a periodically perturbed Eberly-Chirikov pendulum as the key dynamical element responsible for the observed behavior. Numerical simulation of this periodically perturbed pendulum is shown to reproduce the peculiar features of the observed spectra obtained for the full, five-variable model. We discuss the relationship of these studies to the issue of bona fide chaos in a purely quantum-mechanical-level description of the system.

Far-infrared measurements, between 3 and 450 ${\mathrm{cm}}^{\mathrm{-}1}$, of absorption spectra of highly oriented films of Li-DNA and Na-DNA in the temperature range 5–300 K are reported. Five low-frequency infrared-active vibrational modes are observed. The lowest infrared-active mode at 45 ${\mathrm{cm}}^{\mathrm{-}1}$ for Li-DNA and 41 ${\mathrm{cm}}^{\mathrm{-}1}$ for Na-DNA, as observed for the first time, is found to soften upon sample hydration. Studies of the hydration-induced absorption at the low-frequency end of the spectrum also show a pronounced absorption band at about 10 ${\mathrm{cm}}^{\mathrm{-}1}$ that is attributed to relaxation processes. Based on a simple lattice-dynamics model, the description of low-lying vibrational modes of DNA is presented. Eigenvectors of the lowest infrared-active and Raman-active modes are calculated. In addition, the model semiquantitatively describes the influence of hydration on mode frequencies.