We show that, for the high electron currents used in present-day free-electron lasers, spontaneous radiation is distributed according to thermal statistics.

Three-wave mixing equations under parametric approximation have been recast in the form of Bloch equations for optical modes and a new echo analog of optical transient in the space domain is predicted.

It is shown that in the regime of the Raman laser, at the threshold of its excitation, the absorption of the driving field has a singularity.

The electron test particle cross-field diffusion due to thermally excited magnetostatic modes with ergodic field lines is investigated. Estimate shows that in mirror-confined plasmas, the electron transport (and hence the electron thermal conduction) caused by the magnetostatic mode exceeds the convective as well as the classical transport.

The effect of the location of the Gibbs dividing surface on the adsorption and the correct definition of the spreading pressure of a hard-sphere fluid near a hard wall are discussed. The first four exact virial coefficients of the spreading pressure have been calculated. They are compared with those obtained with the use of Percus-Yevick, hypernetted-chain, scale-particle-theory, and superposition approximations. The first three coefficients of the adsorption are calculated. A simpler alternate integral equation for the density profile is proposed with the use of the super-position approximation.

We measured the parallel dielectric relaxation in pentoxybenzylidene octylaniline (50.8), in the nematic, smectic-$A$, and smectic-$B$ phase. This last phase is characterized by a low-frequency relaxation with a small activation energy. Although the Sm-$B$ has a three-dimensional positional ordering, the molecules are mobile as in the nematic and Sm-$A$ phases.

It is shown that the general dispersion relation of electromagnetic surface waves propagating at the interface of certain types of nonlinear media can be obtained exactly without first solving for the field profiles across the boundary.

Systematic corrections to the Glauber approximation for the scattering of charged particles by atoms in general include not only the Wallace correction for potential scattering, but also the effect of target-particle motion and energy change.

Recently, Gupta and Rajagopal [Phys. Rev. A 21, 2064 (1980)] have calculated thermodynamic-exchange energy and potential in an "exchange-only" approximation and later calculated the correlation potential exactly within the random-phase approximation [Phys. Rev. A 22, 2792 (1980)]. In this paper we estimate the effect of screening in an approximate way. The formula obtained for the correlation potential is shown to be the product of two functions, one being that of density and the other being that of dimensionless temperature. The calculated values agree reasonably in the intermediate degeneracy region and are good at higher temperatures and densities. It is shown that the specific heat for the system can also be expressed in terms of the same parameters and the ($\frac{T}{\ln T}$)-type divergence disappears.

Using a simple free-energy functional, we have determined the location of the transition from partial to complete wetting and the thick-thin-film transition line for a model of gaseous argon at a solid carbon dioxide substrate. The wetting transition temperature is significantly higher than that calculated by Ebner and Saam for the same model and the thick-thin transition line lies much closer to the bulk gas-liquid coexistence curve. Our results suggest that thick-film formation will only occur for high temperatures and this is why such films have not been observed in computer simulations and in other recent studies of this model. We show that long-ranged transverse (parallel to the surface) pairwise correlations occur at the edge of the thick and thin films which coexist on the transition line. The range of these correlations becomes infinite at the surface critical temperature and, for the thick film, at the wetting transition temperature.

The triply differential cross section of the electron-impact ionization of atoms is given in a parametrized form, suitable for theoretical computations or for semiempirical fittings. Application of the present formulation is demonstrated. Merits of coplanar measurements are discussed. It is also shown that the coplanar up-down asymmetry of the ejected electron is linear in the scattering angle, or the momentum transfer, of the incident electron for small momentum transfers.

The $\mathrm{Al}{L}_{2,3}\mathrm{VV}$ Auger electrons ejected under ${\mathrm{H}}^{+}$ and ${\mathrm{H}}_2^{+}$ ion bombardments were measured at the backward directions. The observed ratio of the Auger-electron yield per proton for ${\mathrm{H}}_2^{+}$ to that for ${\mathrm{H}}^{+}$ ejected from oxidized aluminum foils increases from 1.0±0.1 to 1.6±0.1 with an increase of the projectile energy from 0.25 to 1.2 MeV/amu, whereas the ratio for oxide-free aluminum foils remains approximately constant (1.1±0.1). First-order perturbation theory fails to reproduce the observed results for both targets.

Resonances in the photodetachment cross sections of ${\mathrm{H}}^{-}$ in a strong dc electric field are studied theoretically in hyperspherical coordinates in the adiabatic approximation. In terms of the variation of one-dimensional effective potentials with electric field for different channels, the experimental results of Gram et al. [Phys. Rev. Lett. 40, 107 (1978)] are interpreted. In particular, the linear Stark splitting of the Feshbach resonance at low fields and the stability of the shape resonance against electric fields up to a few thousand kV/cm are understood from their associated effective potential curves. A new mechanism of field ionization for the "blue-shifted" Stark states is also discussed.

We present results of electron corrrelation calculations in the Briet-Pauli approximation for radiative allowed and forbidden transition probabilities of highly excited Li states, contained in recent schemes for short-wavelength lasers. This is the first quantitative prediction for the phenomenon of relativistic radiative autoionization (RRA). RA has already been singled out as a fundamental deexcitation mechanism which might lead to efficient lasing systems.

Optical second-harmonic generation has been used to deduce the average arrangement and orientation of $p$-nitrobenzoic acid molecules adsorbed at air-silica and ethanol-silica interfaces. An adsorption isotherm for the liquid-solid interface has also been obtained.

Observed depletion of resonance-line emission from heliumlike ${\mathrm{C}}^{4+}$ ions at 308-eV photon energy is associated with photoionization of lithiumlike ${\mathrm{Na}}^{8+}$ ions, as evidenced also by enhanced emission from the latter near the surface of laser-heated sodium-doped carbon targets. The data are analyzed in terms of the total density of ${\mathrm{Na}}^{8+}$ in the absorbing $n=2\mathrm{}$ state, the photoionization cross section, and the relative population density of the radiating $3d$ excited state.

We report quantitative observations of the pretransitional fluctuations in short-range nematic order and the divergence of the magnetic birefringence in the isotropic phase of a lyotropic liquid crystal. The results are analyzed to obtain the anisotropy of the diamagnetic susceptibility and the coefficients in a Landau expansion of the free energy.

A supersymmetric monomer-dimer Hamiltonian is constructed by the assignment of coupled commuting and anitcommuting variables to each lattice site. The resulting super-Hamiltonian generates lattice branched polymer configurations. This relation holds for any value of the fugacity above the critical point and at all dimensions. Although this does not yet prove dimensional reduction beyond perturbation theory, it does provide strong support for its validity for these models in any dimension.

A variant of the renormalization group is applied to the problem of randomly forced fluids studied by Forster, Nelson, and Stephen [Phys. Rev. A 16, 732 (1977)] and others. Amplitude factors (thought to be nonuniversal by some authors) are evaluated and shown to have universal values. Comparisons with closures are made. The possibility of a breakdown of self-similarity and/or universality due to intermittency effects is discussed.

Two average-environment simple cubic lattice models—a refined model and a simple model, both having site-site (segmental) pair Lennard-Jones (LJ) interactions—for molecules composed of rigid cores having semiflexible tails are presented. The calculated values of the following properties at the nematic-isotropic transition for rigid rods of varying length are compared with relevant experimental data for PAA ($p$-azoxyanisole, or 4,4′-dimethoxyazoxybenzene): temperature, core orientational order parameter, nematic density and volume, relative density change, and relative entropy change. The temperature change as a function of volume change at constant order parameter is also discussed. In general, both LJ models give considerably better quantitative agreement with experiment, especially for the temperature and the relative density change, than do the earlier lattice models with hard repulsions, with or without constant segmental pair interaction energies. In most aspects, these LJ models give good quantitative agreement with experiment. These LJ models elucidate the importance of realistic intermolecular potentials, especially the role of soft repulsions, in describing an order-disorder transition between two condensed phases.