Spectra from laser-produced plasmas of Ca, Sc, Ti, V, Cr, and Mn have been recorded in the grazing-incidence region, and the transition arrays 3s-4p, 3p-4s, 3p-4d, and 3d-4f of the neonlike ions have been identified. The measured wavelengths together with the previously observed 3-3 transitions have been used for deriving energy levels of the 2$s^2$2$p^5$3l and 2$s^2$2$p^5$4l configurations. The term structure has been analyzed by means of ab initio and parametric calculations and isoelectronic relations. Coupling conditions have been studied and eigenvectors have been derived. Significant perturbations caused by the 2s2$p^6$nl configurations have been investigated.

The resonance fluorescence from the ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$ I 5535-Å 6${\mathit{s}}^{21}$${\mathit{S}}_0$-6s6p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ transition has been measured as a function of incident intensity using a Doppler-free atomic beam geometry and a single-mode cw dye laser. The upper ${}_{}{}^1{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ level has a weak branch to intermediate metastable D states. A long laser-atom interaction region was used, which ensured that essentially all atoms could be pumped into the D states during their transit through the laser beam. By analyzing the shape of the saturation curve a value for the branching ratio to the 6s5d ${}_{}{}^1{}_{}{}^{}$,3D levels of (3.57±0.38)×${10}^{\mathrm{-}3}$ has been obtained.

We have used a Monte Carlo program to study the Al $L_2$,3 Auger electron spectra induced by 1–10-keV Ar ions at 45° incidence. From a comparison of experimental intensities of the main atomic line and the number of excited sputtered recoils we have evaluated the relative role of symmetric and asymmetric exciting collisions. Angular and energy distributions of the excited sputtered atoms were calculated for different $L_2$,3 vacancy lifetimes in the solid, and from these distributions we obtained the energy shifts of the Auger energies. By including the interaction between the metal surface and the excited sputtered atoms we have reproduced the shape of the main atomic line for various values of the projectile energy.

The nucleus is treated as a source in Kerr-Newman geometry, under the assumption that the angular momentum of the source is equal to the intrinsic spin angular momentum of the nucleus. The spin radius a of the nucleus, which figures in the Kerr-Newman metric, is of the order of the Compton wavelength of the nucleus. The radial functions in Chandrasekhar’s separated Dirac equation in Kerr geometry, are transformed so as to yield a pair of simultaneous first-order differential equations with real coefficients, as in flat space. The magnetic quantum number m appears explicitly in the differential equations, thus lifting the hyperfine splitting degeneracy of Dirac’s equation in flat space.

Stimulated Brillouin scattering in the dye jet inside a linear laser cavity has been investigated and found to be of significant importance for the dynamical behavior of multimode cw dye lasers. At high spectral power densities, it is responsible for a strong coupling of thousands of individual modes into a few mode packets, thus drastically reducing the number of actually existing degrees of freedom of the system. For a decreasing spectral power density, the mode-coupling strength due to stimulated Brillouin scattering lowers, accompanied by an increase of the number of mode packets. At low spectral power densities, additional mode-coupling mechanisms are supposed to account for a stepwise reduction of the number of independently oscillating mode packets. As an interesting application, the spectroscopic technique of intracavity optical-optical double resonance is discussed and demonstrated.

A continuous-wave maser operating on a two-photon transition between Rydberg levels is expected to oscillate with about one atom and a few tens of microwave photons at any time in its superconducting cavity. We analyze in detail the characteristics of this new microscopic quantum electronics device presently under construction in our laboratory.

The problem of fundamental laser line broadening due to random spontaneous emission of radiation and amplification of thermal radiation noise is analyzed in terms of a classical fluctuating field phasor model. We derive a general expression for the intrinsic linewidth, given in terms of the spectral power of the radiation noise source, which can be classical or quantum mechanical in nature. In the case of a two-level atomic laser, we recover by the use of Einstein relations, the traditional linewidth formula of the Schalow-Townes form. In the case of the free-electron laser (FEL), using the explicit expression for the spontaneous emission, we present calculation of the laser linewidth by purely classical methods. The result agrees with the one obtained in the framework of a quantum-mechanical model. By using ‘‘extended Einstein relations’’ which are applicable to classical radiators, we show that a Schalow-Townes-type formula can also be obtained for the FEL. The theory predicts extremely narrow intrinsic linewidth ${(10\mathrm{}}^{\mathrm{-}7}$ Hz) for cw FEL’s with parameters similar to those of the FEL experiment of Elias et al.

The temporal evolution of the transmitted light field is computed for a high-density gas of two-level atoms, which is externally excited by an amplitude-modulated field in resonance with the atomic transitions. The transmitted field is shown to exhibit a chaotic transient and a cascade through different phase-locked orbits. Due to the asymmetry of these orbits, the field develops a nonzero average value even in the absence of a bias.

A field theory of non-Born-Oppenheimer vibronic interaction in a molecular system is formulated using a differential geometrical study of quantum molecular dynamics [A. Tachibana and T. Iwai, Phys. Rev. A 33, 2262 (1986)]. In contrast to the conventional approach of many-body formalism, the present approach stresses the finite-system aspects of the theory. The formalism is, of course, general and exact and applies to infinitely large systems. Remarkably, a new vibronically induced interelectron attraction is revealed, which is not brought about by the conventional mechanism of electron-phonon coupling in condensed-matter physics. It is shown that the ‘‘sign’’ of the vibronic interaction with respect to the Coulombic repulsion is - and is not + in the conventional electron-phonon coupling model. The physical origin of the newly found interelectron attraction is clarified in terms of the ‘‘instantaneous’’ nature of vibronic interaction and the primordial ‘‘spin-flip’’ mechanism of non-Born-Oppenheimer electron scattering processes [A. Tachibana, K. Hori, and T. Yamabe, Chem. Phys. Lett. 112, 279 (1984)]. This predicts a ‘‘hidden’’ vibronic mechanism of superconductivity.

It is demonstrated that for an optical pulse propagating along an optical fiber the rms pulse width varies parabolically with distance, irrespective of initial pulse form and frequency chirp variation. Furthermore, the result is true to arbitrary dispersive order and should prove a very useful tool in determining the information-carrying capability of long-distance optical-fiber transmission systems.

A spinless hydrogen atom coupled to the electromagnetic field is considered within the context of nonrelativistic quantum electrodynamics. The atom-field interaction is taken in the minimal-coupling form and the Coulomb gauge is used. When the coupled system is in its ground state the electromagnetic field fluctuates away from the vacuum state and the atom has virtual admixtures from its uncoupled lowest eigenstate. The electric- and magnetic-field-energy densities that arise from the fluctuations are determined as functions of the distance from the atom. The relationship between these field-energy densities and the retarded long-range van der Waals forces is also discussed.

We consider a three-level atomic system driven strongly on one transition and weakly on the other. The excited state on the weak transition is assumed to be metastable. We give an analysis of the fluorescence from the strong transition in terms of the elementary probability density $p_{[0}$,t)(${\mathrm{t}}_1$,$t_2$,..., $t_n$) which gives us the probability density that exactly n photons are emitted at times $t_1$,$t_2$,...,$t_n$ by the atom in the time interval [0,t). We show that $p_{[0}$,t) essentially factorizes into products of conditional densities c̃(τ) that, given a photon is emitted at time zero, the next photon emission occurs at time τ. This enables a simulation of the individual photon emissions to be given which shows directly the existence of prolonged dark windows in the fluorescence corresponding to the shelving of the electron in the metastable state or ‘‘quantum jumps.’’

Exact formulas for the effective eigenvalue characterizing the initial decay of intensity correlation functions are given in terms of stationary moments of the intensity. Spontaneous emission noise and nonwhite pump noise are considered. Our results are discussed in connection with earlier calculations, simulations, and experimental results for single-mode dye lasers, two-mode inhomogeneously broadened lasers, and two-mode dye ring lasers. The effective eigenvalue is seen to depend sensitively on noise characteristics and symmetry properties of the system. In particular, the effective eigenvalue associated with cross correlations of two-mode lasers is seen to vanish in the absence of pump noise as a consequence of detailed balance. In the presence of pump noise, the vanishing of this eigenvalue requires equal pump parameters for the two modes and statistical independence of spontaneous emission noise acting on each mode.

We apply the so-called ‘‘synthetic’’ nonequilibrium molecular-dynamics method to the calculation of the self-diffusion constant of a Lennard-Jones fluid at a number density of 0.85/${\sigma }^3$ and a temperature of 1.08ɛ/$k_B$ (where ɛ and σ are the energy and length parameters of the potential and $k_B$ is the Boltzmann constant). By comparing with the Green-Kubo calculation for the same state of the system and for the same number of particles, N, we find the latter calculation to yield more precise values of the self-diffusion constant for a given number of molecular-dynamics time steps. Even at small values of the diffusion current, a nontrivial time is needed for the nonequilibrium calculation to reach the steady state. For larger values of the driving force, the steady-state flow appears to become unstable and evidence of a secondary flow pattern is presented. The presence of these instabilities acts as a limit to the range of the driving force for which the steady-state method can be applied. With increasing N the range of stable values of the diffusion current density decreases. For the Green-Kubo calculations, the N dependence of the self-diffusion constant is found to be anomalous for N=108, with the 1/N dependence only exhibited for at least 500 particles. The nonequilibrium results, while approximately independent of N for 108 and 500 particles, are found to have a similar anomalous N dependence when we extend the calculations to 1372 particles, thereby bringing the Green-Kubo and nonequilibrium results into agreement in the large-system limit.

A new time-dependent atomic model is presented. In the model, called the hybrid-atom model (HAM), the energy-functional form of the population probability obtained from the average-ion model is used to estimate the level population of ions having charge different from the average ion. In medium-Z plasmas HAM gives results similar to the collisional-radiative (CR) model. The required computation time is comparable to the average-ion model even for high-Z plasmas. In these plasmas the CR model becomes impracticable. Though the model partly uses the average-ion model, the x-ray emission calculated is significantly different.

Textured convective flow patterns in a large cylindrical layer are studied using digital image processing methods to measure the wave-vector field q(r), a slowly varying two-dimensional field that may be used to characterize complex patterns quantitatively. We describe in some detail the development of this method and its application to the analysis of both steady and time-dependent patterns. The variation of the convective textures with ε=(R-$R_c$)/$R_c$, where $R_c$ is the critical Rayleigh number, is studied using quantities derived from the wave-vector field, such as its divergence and its orientation at the boundary of the container. We also find a useful criterion for the stability of convective patterns: Time-dependent patterns usually have a distribution of wave numbers that lies partially outside the predicted stable band for an infinite layer. Measurements of the Swift-Hohenberg Lyapunov functional show that this quantity varies by up to 25% for different stable patterns at the same value of ε. .AE

All the excited adiabatic electronic states of ${\mathrm{Na}}_2$ dissociating into 3d+4s, 4p+3s, and 5s+3s atoms are calculated using a nonempirical pseudopotential, a flexible basis set, and the exact valence configuration-interaction treatment. Together with a highly precise work [G. H. Jeung, J. Phys. B 16, 4289 (1983)], where all the electronic states dissociating into 3s+3s, 3p+3s, and 4s+3s atoms have been calculated, this work reveals the lowest 38 electronic states of ${\mathrm{Na}}_2$. Wherever possible, the comparison of the present data with the recent spectroscopic observations shows excellent agreement. The majority of the theoretically predicted states remains to be found experimentally.

We present calculations for the analysis of torsional oscillator measurements of the mechanical properties of viscoelastic fluids and solids. The usefulness of this measurement technique is analyzed and discussed in detail. A right circular cylinder is chosen as a well-defined geometry for accurate calculations. Exact expressions for calculating the fluid viscosity and elasticity from the oscillator response in this geometry are presented and discussed. We believe this to be the first exact treatment of the problem. Simplified expressions valid for certain special cases are presented for ease of calculation and compared to those previously obtained. The range of operation and optimal oscillator designs for general applications are suggested. Finally, use of this technique for measuring the frequency dependence of viscoelastic properties is also examined.

Results of a numerical simulation of unstable two-phase displacement in a Hele-Shaw cell are presented and compared with experimental data. Previous flow simulations, while reproducing many of the qualitative features of viscous fingering, consistently underpredicted the asymptotic value of finger width observed in a linear channel. We introduce here a modified boundary condition, as indicated by an asymptotic analysis of Bretherton, so that the pressure jump at the fluid interface is now a function of the instantaneous value of the particle velocity. This modification makes the imbedded problem nonlinear; it can, however, be treated successfully using Newton iteration. The results of the model depend parametrically on both the cell depth-to-width ratio and the capillary number of the displacement. Most of the discrepancy between theory and experiment is removed except at high speeds, where the numerically predicted finger width is somewhat higher than is observed. The basic qualitative features of the fingering phenomenon remain unchanged by the addition of the new effect.

The use of unresolved transition arrays for the determination of plasma temperature is described. A compact low-resolution spectrometer, based on this technique, which yields both temporally and spatially resolved data, has been constructed. It may be developed easily into a real-time device.