Complex dressed states and photoelectron spectra are considered for a model system containing two discrete states that are coupled by separate lasers to a continuum that supports a resonance such as an autoionizing state. Spontaneous radiative decay from the structured continuum has been included and its effects are examined. It is shown that population can be trapped within the model atom even when radiative decay is included provided (1) the two Fano q values which characterize the discrete-state–continuum interactions are equal, and (2) the two-photon resonance condition is satisfied.

Resonant photoelectron spectra of Kr have been taken in the photon-energy ranges of the 3$d_{5/2}$→5p,6p and 3$d_{3/2}$→5p excitations. The spectra, which closely resemble normal ${\mathrm{Kr}}^{+}$ 3$d^{\mathrm{-}1}$ Auger spectra, illustrate the importance of ‘‘spectator’’ Auger-like decay for inner-shell resonances, in which the initially excited electron does not participate in the core-hole deexcitation process, except to respond to the change in the atomic potential. Possible assignments for some of the spectator decay channels are discussed based on photoemission intensity measurements at the different 3d resonances. These assignments suggest that shake-up (e.g., 5p→6p) of the ‘‘spectator’’ electron during the decay process is not quite as important as previously suspected. The resonance profiles of some of the more intense satellites have been determined over the 3d→np resonances. Very small resonance effects also were observed in the partial cross section for 4p subshell ionization, which produced asymmetric Fano-type profiles. The 4p angular distribution, in contrast, exhibits a pronounced effect in the resonance energy range. The 4p results demonstrate that nonspectator autoionization also is present.

A detailed study of above-threshold ionization processes in xenon and krypton is reported. Using well-characterized pulses of 1.06- and 0.532-μm radiation under carefully controlled experimental conditions, measurements of the energy and direction of photoelectrons from Xe and Kr as a function of laser power and polarization were made. Conclusions about the role of ponderomotive potentials in the determination of much of the phenomenology are presented.

Pair creation by an intense linearly polarized pulse in the vicinity of a nucleus is considered. It is shown to be negligibly small for all laser intensities for essentially all frequencies. Some novel theoretical effects are obtained from the relativistic generalization of the ponderomotive potential.

Several fluorescence and excitation bands, arising from transitions from and to the H, I, and J states of ${\mathrm{Hg}}_2$, have been investigated using laser-induced fluorescence techniques. The upper and lower states have been assigned for each band and their analysis has yielded a number of vibrational constants. Measurements of relative intensities and studies of band shapes have made possible the accurate location of various electronic molecular states, relative to one another, on the potential energy diagram.

We apply a general formalism for the separation of rapid and slow time scales in linear evolution equations to three-state atoms with a strong and a weak radiative transition. This leads to an expression for the intensity correlation function that constitutes a good approximation on both time scales. This result can also be translated into an expression for the waiting-time distribution for the next photon emission after a previous one. The slow evolution is expressed in two rate constants, which determine the statistical distribution for dark and bright periods in the fluorescent emission. The result is applied to various configurations of the radiative couplings between the three states.

Extensive measurements have been performed to determine the absolute energies of the n ${\mathrm{}}^2$$S_{1/2}$ (n=8–31), n ${\mathrm{}}^2$$P_{1/2}$ (n=6,9–80), n ${\mathrm{}}^2$$D_{5/2}$ (n=5,7–36), n ${\mathrm{}}^2$$F_{5/2}$ (n=6–65), and n ${\mathrm{}}^2$$G_{7/2}$ (n=6–54) levels of Cs by using nonresonant and resonantly enhanced Doppler-free two-photon spectroscopy. The excitation mechanisms employed include resonantly enhanced dipole-quadrupole and quadrupole-quadrupole transitions. All energies were measured directly with respect to the 6 ${}_{}{}^2{}_{}{}^{}S_{1/2}^{}{}_{}{}^{}$ ground state. The laser wavelengths were measured by high-precision Fabry-Perot interferometry yielding an uncertainty of 0.0002 ${\mathrm{cm}}^{\mathrm{-}1}$ for most Cs levels. Ionization energies derived by fitting the modified Ritz formula to each of the five series observed coincide within 0.000 05 ${\mathrm{cm}}^{\mathrm{-}1}$. Taking account of possible systematic errors, the Cs ionization energy is 31 406.467 66(15) ${\mathrm{cm}}^{\mathrm{-}1}$.

We have developed a quantum-mechanical formalism which permits the treatment of light propagation within the conceptual framework of quantum optics. The formalism rests on the calculation of the momentum operator for the radiation field, and yields directly a description for the spatial progression of the electromagnetic waves. In this paper we give a quantum-mechanical treatment for refraction and reflection by applying our formalism to propagation through a linear dielectric. The fidelity with which this formalism reproduces all results known from classical optics demonstrates its validity.

Pulses from Nd:YAG lasers (where YAG represents yttrium aluminum garnet) were amplified up to 20 times by noncollinear mixing with a coherent pump wave in silicon. Amplification of long pulses (about 16 ns) was obtained with intersection angles up to 2° whereas angles larger than 10° are possible with short pulses (50 ps). The effect is theoretically described by self-diffraction at a laser-induced dynamic free-carrier grating.

The effect of an intense pump beam on the intensity of the phase-conjugated emission is studied in the case of a three-level atom. We first extend to the case of cross-polarized pump beams the dressed-atom model that we have presented previously [Phys. Rev. A 34, 4008 (1986)] for the case of two-level atoms. The range of validity of our theory is Γ (natural width) <${\Omega }_1$ (Rabi frequency of the intense pump) <ku (Doppler width). We have studied the line shape in degenerate four-wave mixing, the influence of a static magnetic field, and the resonances that appear in nondegenerate four-wave mixing. Experiments are done in a neon discharge using cw dye lasers. The experimental results are in good agreement with the theoretical predictions. In degenerate four-wave mixing, we have shown that the saturating dip disappears when the weak beams have orthogonal polarizations. In the presence of a static magnetic field and in the nearly degenerate case, narrow resonances corresponding to transitions between energy levels of the dressed atom are observed. The intensity and the width of these resonances are in very good agreement with the predictions of the theoretical model.

We investigate the existence of nonuniform thermodynamic states of classical fluids with purely repulsive finite-range interaction, such as that of hard spheres. Both free energy and nonuniform profile are obtained in the strict limit of an infinitely large spatial dimension. We establish the density at which the uniform state undergoes a Kirkwood instability, and provide a basis for the surmise that this instability leads continuously to an ordered lattice.

Petrosky has shown that it is possible to continue analytically the nonresonant generating function in Lie transform theory and thereby treat resonant interactions in Hamiltonian systems. I will show that this formalism can be derived from the subdynamic theory proposed by the Brussels school. In addition to discussing the relationship between these two formalisms, some of the consequences of the resonant theory in wave-particle interactions are explored. In particular, I derive a complex K-χ theorem, which relates the resonant ponderomotive Hamiltonian to the imaginary part of the susceptibility of the plasma. This provides a conceptually appealing generalization of the nonresonant results. Finally I discuss other possible applications of the resonant Lie transform theory in plasma physics.

The dynamical behavior of x-ray emissions ranging from 90 to 110 Å generated from laser plasmas is studied and x-ray energies are measured for various target materials with the atomic number from 13 to 82. With the use of a picosecond YAG laser (YAG represents yttrium aluminum garnet), characteristic decay times can be obtained accurately and varied from 100 to 800 ps as functions of target materials. It is also found that the decay times are well correlated with x-ray energies as functions of the atomic number. From this correlation, the atomic-number dependence of decay times can be explained by considering that line x rays are emitted mainly through the radiative recombination processes. X-ray decay times can be measured correctly using a picosecond laser. The dynamical behavior of x-ray energies is explained by the computational result performed for aluminum as an example in the framework of a transient collisional radiative model.

Various characteristics of x-ray emission from laser plasmas produced by a picosecond YAG laser (where YAG represents yttrium aluminum garnet) are investigated in the wide wavelength band ranging from 10 to 2000 Å from the point of view that emitted radiation from laser plasmas is applied to many purposes, such as laser fusion, x-ray lasers, x-ray sources, and solid-state physics. In this wide wavelength band, extremely different dependences of x-ray energies on input laser energies are made clear. With a decrease of the wavelength, the slope of the dependences increases. Decay times of emitted x-rays from laser plasmas are approximately proportional to the wavelengths. Computational studies are also performed in the framework of a transient collisional radiative model in order to explain the experimental results.

We present numerical and theoretical results for self-trapped states in the lossless, saturably nonlinear Klein-Gordon equation $u_{\mathrm{tt}}$-$u_{\mathrm{xx}}$=-u/(1+$u^2$). A simple approximate analytic theory is developed which agrees well with self-trapped states found in simulations to emerge from certain types of localized, stationary, one-sided ‘‘displacements,’’ u(x,0)≥0, $u_t$(x,0)=0. The stability of theses states to strong perturbations is studied by pulse-collision simulations, using for the perturbation one of the two traveling-wave pulses generated in the fast dissociation of a highly unstable initial displacement. The self-trapped states are highly stable, exhibiting a shape change and centroid shift after collision, but little energy loss or change of period.

The small-amplitude, long-wavelength perturbation expansion of the water-wave equation has been extended to the fourth order of approximation for overtaking collisions of solitary waves. It is found that collisions of solitary waves generate, besides the dispersive wave train reported by us earlier [Q.-s. Zou and C.-H. Su, Phys. Fluids 20, 2113 (1986)], a single wavelet consisting of a positive headwave followed by a tailwave of the same shape but of negative value. This wavelet propagates with the linear wave speed and in the opposite direction to that of the solitary waves and the dispersive wave train. A model equation which has all the relevant properties pertaining to the generation of these waves from our perturbation analysis is proposed. Numerical calculations of this model equation confirm the perturbation results.

A new theory of dynamic correlations in a strongly coupled, classical one-component plasma (OCP) is developed within the generalized viscoelastic formalism. Fully convergent kinetic equations for the strongly coupled OCP are thereby derived with the aid of a fluctuation-theoretic formulation of the collision integrals. The dynamic structure factor S(k,ω) and the coefficient η of shear viscosity are calculated both in the ordinary fluid state and in the metastable supercooled state through a self-consistent solution to the kinetic equation. It is shown that the numerical results in the ordinary fluid state agree well with other theoretical and molecular-dynamics simulation results. A possibility of the dynamic glass transition is predicted in the supercooled OCP through the analyses of the variation in η, the quasielastic peak in S(k,ω) and the behavior of the self-diffusion coefficient; the prediction is compared with those in the glass-transition theories for other systems. Relevance to laboratory experiment is examined in terms of the metastable-state lifetimes against homogeneous nucleation of the crystalline state.

The Helmholtz free energy F of the hard-sphere bcc solid is calculated with use of two techniques: the weighted-density-functional approximation (WDA) and Monte Carlo simulations, using the coupling-constant technique of Frenkel and Ladd [J. Chem. Phys. 81, 3188 (1984)] to obtain F. Since the hard-sphere bcc structure is unstable to shear, the WDA calculations are carried out within a class of density profiles which exclude the shear mode and single-occupancy cell constraints are imposed in the simulation studies. The two results for F are in substantial agreement with each other and show that at sufficiently high densities the (shear-stabilized) bcc phase has a free energy lower than that of the liquid but higher than that of the fcc solid, while at lower densities the liquid is lowest in free energy followed by the bcc and then the fcc solid. Also, at fixed density the mean-square displacements of the bcc atoms are larger than those of the fcc atoms as a result of the relative openness of the bcc structure. The WDA results compare very favorably to other density-functional calculations of the bcc phase carried out within the same constrained class of density profiles which either fail to predict the existence of a bcc phase or predict a stable phase only at very high densities and having a free energy larger than even the liquid. In an appendix, we (i) present fcc and bcc free energies using improved liquid-state input data and (ii) allow for non-Gaussian density profiles in the solid. Both alterations yield only slightly lower (<2%) free energies than determined using Percus-Yevick liquid data and Gaussian profiles.

We study how the introduction of a two-body interaction changes the thermodynamic properties of the free Bose gas in a weak (scaled) external field. We show that, in the van der Waals limit, the thermodynamic pressure always is a $C^{\infty }$ function of the density in one and two dimensions, while this is not so in higher dimensions. The phase transition to the superfluid phase in the latter case is discussed in more detail by looking at the local densities. We also show that the van der Waals limit for this system does not correspond to the usual mean-field approximation.

Thermodynamic perturbation theory and the Kirkwood-Salsburg correlation function identities are used to study nearest-neighbor lattice gases with certain weak symmetry-breaking many-body interactions. It is shown that such systems may be mapped onto symmetric models by the introduction of suitable effective interactions and a shifted chemical potential, both of which depend explicitly on the temperature and fugacity of the original model. In the critical region, such a thermodynamic-state dependence implies the existence of a thermal scaling field which depends on the bare chemical potential, and this ‘‘field mixing’’ leads to a breakdown in the classical law of the rectilinear diameter. These results give a microscopic interpretation to a field-theoretic renormalization-group analysis which derives such a diameter singularity from the presence of terms cubic and higher in the order parameter and its gradients in an asymmetric Landau-Ginzburg-Wilson Hamiltonian. For a primarily repulsive three-body potential like the Axilrod-Teller interaction in classical insulating fluids, and in comparison with recent experiments, the analysis correctly describes the observed trends in the critical and near-critical behavior of the diameters with increasing particle polarizability.