The steady-state statistical properties of the single-mode laser with multiplicative white-noise loss fluctuations are investigated. Analytic expressions for the intensity distribution and its moments are derived and it is shown that the multiplicative noise significantly modifies the laser characteristics. These predictions are then tested by photoelectric measurements of a He:Ne laser with fluctuating loss. Good agreement between theory and experiment is obtained.

A dynamical bifurcation in which the control parameter is continuously swept through the bifurcation point is characterized in terms of a first-passage-time distribution. The generating function associated with this distribution is calculated in the cases of slow and fast sweeping rates. Our results are compared with experimental findings in an Ar laser with time-dependent cavity losses and with earlier numerical and analogical simulation results. The meaning of a delayed bifurcation in the stochastic framework presented here is elaborated.

We present experimental and theoretical results describing the presence of radiative-decay-induced narrow resonances in systems which do not conserve population, alignment, or orientation. We show how spectroscopic line-shape analysis of the nonlinear response can be used to determine all of the relaxation parameters characterizing a two-level atom.

We use random-tempering formulas and explicitly correlated Slater-type geminals to calculate the S and P bound-state energies of the muonic molecules xyμ, where x,y=p,d,t. The final binding energies are accurate to about 1 μeV or better except for the weakly bound tdμ(11) state. For this state we get a binding energy of 0.660 1721 eV, which is better than any previous calculation.

Hong and Mandel’s concept of higher-order squeezing [Phys. Rev. Lett. 54, 323 (1985); Phys. Rev. A 32, 974 (1985)] is applied to the generalized multiphoton Jaynes-Cummings model of a single two-level atom interacting with an initially coherent cavity-field mode. The fourth-order squeezing is examined. The field is shown to be intrinsically squeezed to this order for the photon multiple m≥4.

A semiclassical theory of stimulated processes in dielectric spherical particles is formulated. The theory applies to the small-signal regime and to isotropic (but radially nonuniform) pumping. Iterative treatment of the pumped-medium susceptibility by scattering theory demonstrates the basic features observed experimentally by Chang and co-workers [H. M. Tzeng, K. F. Wall, M. B. Long, and R. K. Chang, Opt. Lett. 9, 499 (1984); S. X. Qian and R. K. Chang, Phys. Rev. Lett. 56, 926 (1986)], namely, the drastic reduction of the threshold for lasing and multiorder stimulated Raman processes, and the frequency pulling from Mie resonances of the inactive medium.

Four time correlation functions of a Lennard-Jones (LJ) fluid at a reduced density of $n^{\mathrm{*}}$=n${\sigma }_{\mathrm{LJ}{}^3=0.845\mathrm{}}$ and a reduced temperature of $T^{\mathrm{*}}$=$k_{\mathrm{B}\mathrm{T}/{\varepsilon }_{\mathrm{LJ}=1.71\mathrm{}}}$ have been determined numerically using molecular dynamics. They were computed as a function of wave number k for reduced wave numbers 0≤k${\sigma }_{\mathrm{LJ}<15\mathrm{}}$ and for reduced times 0≤t/${\tau }_{\sigma }$<2.6, where ${\tau }_{\sigma }$ is an average collision time. From these four, all 25 correlation functions can be derived between three conserved and two nonconserved quantities: the number density, energy density, longitudinal velocity, momentum flux, and energy flux, respectively. They can be fitted consistently by five exponentials that correspond to the five eigenmodes of a 5×5 k-dependent, but not t-dependent, matrix based on the above-mentioned five quantities. Three of these eigenmodes are extensions of the usual hydrodynamic modes and suffice to describe the density-density correlation function alone. A comparison with previous work on Lennard-Jones, noble-gas, and hard-sphere fluids is made.

The density dependence of Δn=0 (4-4) transitions for rare-earth-metal ions isoelectronic with Cu i has been studied over a large density domain ${10}^{13}$–${10}^{21}$ ${\mathrm{cm}}^{\mathrm{-}3}$ by measuring the spectral emissions from these ions in tokamak and laser-produced plasmas and comparing them with theoretical models. The computational techniques used for the atomic parameters in the collisional radiative model of the level populations were checked in the low-density range ∼${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}3}$ by analyzing the spectra of ${\mathrm{Eu}}^{34+}$ and ${\mathrm{Yb}}^{41+}$ emitted from a tokamak plasma. Then laser-produced spectra of ${\mathrm{Sm}}^{33+}$ and ${\mathrm{Yb}}^{41+}$ were analyzed using similar models for the density dependence of the line ratios in the high-density region ${10}^{19}$–${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$. The theoretical models included the effect of cascading from n=5 states on the population of the n=4 levels. In addition, optical depth effects on the line intensities were considered for the high-density laser-produced plasmas. The present work demonstrates the potential of highly ionized rare-earth-metal atoms as electron-density diagnostics in high-density plasmas. In particular, all along the isoelectronic sequence from Z=59 to Z=70 the two density-sensitive transitions 4d ${}_{}{}^2{}_{}{}^{}D_{5/2}^{}{}_{}{}^{}$–4f ${}_{}{}^2{}_{}{}^{}F_{7/2}^{}{}_{}{}^{}$ and 4p ${}_{}{}^2{}_{}{}^{}P_{3/2}^{}{}_{}{}^{}$–4d ${}_{}{}^2{}_{}{}^{}D_{5/2}^{}{}_{}{}^{}$ remain close to each other and are unblended with other lines, and thus their ratios represent particularly attractive density diagnostics.

We study the charged–hard-sphere model of a fused salt near a planar electrode, using a density-functional theory of inhomogeneous electrolytes. The results at relatively high temperatures show an oscillating charge distribution near the electrode, suggesting that near solid-liquid coexistence, the electrode is ‘‘coated’’ by a few atomic layers of the solid phase, analogous to wetting phenomena at liquid-vapor coexistence. At lower temperatures, we observe the growth of a macroscopically large ordered (solidlike) phase that is separated from the bulk fluid by an interface that extends over many molecular layers. Among other things this result shows, for the first time in the literature, that a density-functional theory is capable of producing a thermodynamically stable, ordered phase without the need of putting in any crystallographic symmetry at forehand.

We measured the line profiles of the Δn=0,n=2 lines of C v produced when a ruby laser was focused (≥${10}^{12}$ W/${\mathrm{cm}}^2$) onto a polyethylene target. Line profiles were measured at 3 mm from the target surface where the electron density is of the order of ${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$ as inferred from a folded wave-front shearing interferometric technique and the line profile of the 3434-Å line of C vi. After fitting the data to profiles calculated considering the different Stark and Doppler contributions to the line, we found that the calculated profile for the 3526-Å line of C v is considerably narrower than the experimental result and this discrepancy is common to all the Δn=0,n=2 lines. Judging from the fact that the ratio of the experimental widths of the different lines is proportional to the respective ratio of wavelengths this effect should be related to the ion motion. The presence of hydrodynamic turbulence causing the profile to have a large effective Doppler temperature approximately equal to 600 eV may explain this result.

We measured space- and time-resolved profiles of ${\mathrm{H}}_{\mathrm{\alpha }}$, ${\mathrm{H}}_{\mathrm{\beta }}$, and ${\mathrm{L}}_{\mathrm{\delta }}$ of C vi, in a laser-produced carbon plasma, at the time when the intensity of C vi lines is the highest. Comparing the measured Stark widths of $L_{\delta }$ and $H_{\beta }$ with calculated values which consider the effects of ion dynamics, we inferred an electron density of ${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$ on target. Using that electron density and recent results for the Stark width of the $H_{\alpha }$ fine-structure components, we fitted an experimental profile of this line to a calculated profile consisting of a superposition of Voigt profiles placed at the positions of the three strongest components. The Gaussian contribution to the profile is a combination of a calculated instrumental width and a Doppler width extrapolated from the measured widths of C v lines in the near ultraviolet. Our results suggest that under conditions similar to those in the x-ray laser experiments, fine-structure splitting, Doppler broadening, and Stark effects are about equally important for $H_{\alpha }$. We also present results from time-integrated spectra that support our time-resolved observations.

Inviscid incompressible two-dimensional fluid vortex systems are shown to be interesting classical statistical-mechanical systems. The density of states of such systems is ‘‘bounded,’’ leading to negative temperature states. As the number of vortices increases, the density of states of unit-disk vortex systems fails to develop a strong peak as the number of vortices in the system increases. The third law of thermodynamics does not hold.

Radiation from a hot plasma is produced by inelastic collisions of energetic electrons with highly ionized ions. In each collision these electrons lose a large amount of energy, which, in large part, is lost from the plasma as radiation and replenished by heating. Radiative cooling, principally in the tail of the electron distribution function, and heating, generally below thermal energies, modify the electron-energy distribution. This modification in turn affects the plasma properties. For a z-pinch neon plasma around ${10}^{19}$ ${\mathrm{cm}}^{\mathrm{-}3}$ density and 200 eV temperature the radiative power decreases up to about 20%, although the radiation rate for an individual line could decrease by up to 100%.

The onset of chaotic convection in large-Prandtl-number fluids has been found to occur in the form of elongated cells with aperiodic boundary-layer instabilities. The dynamics of this phenomenon has been monitored in the physical domain, and also in the spectral and phase spaces. In order to describe more precisely the underlying mechanisms of chaotic thermal convection, we find it useful to introduce the notion of ‘‘thermal attractor’’ in the physical domain and to conduct a systematic study of the evolution of the spectral energy surfaces. We propose here a relationship between this thermal attractor and the presence of a strange attractor in the phase space.

An R-matrix variational principle is presented in which the value of the function on the boundary surface is specified rather than its slope or logarithmic slope. Such a boundary condition appears to be convenient for treatment of the ionization process because, in principle, a boundary function can be built up by linear combination of inside solutions. Explicit treatments of potential and multichannel scattering are given as well as a numerical application to a model problem to demonstrate the method.

Results are given of a ${\mathrm{CO}}_2$-laser scattering experiment on lower-hybrid waves at a frequency of 2.45 GHz performed in the Frascati tokamak. Signals are found in the location predicted by a ray-tracing code. The $N_{?}$ spectrum [$N_{?}$=(c/ω)×$K_{?}$, where $K_{?}$ is the component of the wave vector in the magnetic field direction and ω/2π is the wave frequency] of lower-hybrid waves is determined at the plasma center showing a depletion of the high-$N_{?}$ with respect to the launched spectrum in the scattering volume.

We have investigated the particle-guiding center motion (across a strong magnetic field) caused by a time-dependent electrostatic field. Two different nonlinear Hamiltonian systems of 1.5 degrees of freedom have been used. The Hamiltonian is proportional to the electrostatic potential, which is defined through its spatial Fourier spectrum in two dimensions. A $k^{\mathrm{-}3}$ power-law spectrum (k is the wave vector) and random-phase shifts have been chosen to model the spatial dependence of the electrostatic drift-wave turbulence observed in several tokamaks. The equations of motion have been solved numerically. When the average electric field amplitude is larger than a threshold value, the particle trajectories become chaotic at large scale and a diffusion across the magnetic field sets in. The diffusion coefficient D has been measured for different values of the average electric field amplitude A. The classical (quasilinear) scaling has been found at small A, D∝$A^2$, while a transition to the Bohm scaling is found at higher amplitudes, D∝A. A recently proposed theoretical treatment of the same problem has been applied to our models and the theoretical predictions have been compared to the results of numerical simulations. For relative diffusion, the theoretical prediction of the so-called ‘‘clump effect’’ has been well confirmed by numerical simulations. Theory and simulation are in qualitative agreement for the dependence of D on A, but some quantitative discrepancies exist; their nature is discussed.

We show that certain extended dissipative dynamical systems naturally evolve into a critical state, with no characteristic time or length scales. The temporal ‘‘fingerprint’’ of the self-organized critical state is the presence of flicker noise or 1/f noise; its spatial signature is the emergence of scale-invariant (fractal) structure.

The behavior of a system of many coupled maps is examined numerically. The maps used are selected so that a single map has entirely trivial mode-locking behavior and only the coupled system displays subharmonic mode locking. Three variants of the map are examined, each with different results. None of the behaviors appears to be simply related to that displayed by a circle map, which exhibits mode-locking behavior typical of that found for systems with one effective degree of freedom.

Absolute cross sections for electron-impact single ionization of ${\mathrm{Kr}}^{8+}$ and ${\mathrm{Xe}}^{8+}$ ions were measured for energies below the ionization thresholds to 1500 eV using the crossed-beams method. A significant fraction of the ${\mathrm{Kr}}^{8+}$ and ${\mathrm{Xe}}^{8+}$ ion beams were in metastable configurations. Configuration-average distorted-wave calculations for ions in the ground and first-excited configurations are compared to the experimental data. For both ions in this study, the excitation-autoionization contribution to the total ionization cross section is found to be much larger for ions in the first-excited configuration, which includes metastable levels, than for the ground-state ions. Maxwellian rate coefficients were calculated for ${\mathrm{Kr}}^{8+}$ and are compared to published results.