Spectra of the zinclike ions Rb viii, Sr ix, Y x, Zr xi, Nb xii, and Mo xiii were excited with sparks and laser-produced plasmas and observed with normal- and grazing-incidence vacuum spectrographs. Almost all levels of the 4$s^2$, 4s4p, 4$p^2$, 4s4d, 4s5s, 4s5p, 4p5s, and 4s5d configurations were established in these ions. Several 4s4f ${}^3$F–4s5g ${}^3$G transitions of Nb xii and Mo xiii were also identified. The observed energy levels were interpreted by means of least-squares parametric fits and Hartree-Fock calculations. The ionization energies were determined as 132.79(25) eV for Rb viii, 158.33(25) eV for Sr ix, 185.77(37) eV for Y x, 214.86(37) eV for Zr xi, 246.11(37) eV for Nb xii, and 279.09(50) eV for Mo xiii.

The energy loss of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ ions in Ni, Ag, and Cu has been investigated via the inverted Doppler-shift attenuation technique in the energy range up to 3.1 MeV. Excited ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ nuclei were produced in the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^3$He,p) ${}^{14}$${\mathrm{N}}^{\mathrm{*}}$, and energy-loss information was obtained from the analysis of the Doppler-broadened 2.313-MeV γ-ray line, observed with a Ge(Li) detector. This analysis also yielded the lifetimes of the levels at 2.3 and 3.9 MeV in ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, which were determined to be 97.7±5.5 and 5.6±1.1 fs, respectively, in reasonable agreement with previous measurements and theoretical calculations. The stopping cross sections obtained for all three stopping media are compared with existing theoretical calculations, especially with regard to the oscillations with the atomic number of the stopping medium.

A theory of Rydberg and continuum states in intense laser fields is developed based on the observation that the effect of laser radiation can be described in a scattering formulation as a finite-volume interaction coupling Coulomb-type fragmentation channels. In particular, laser-induced couplings may be incorporated in a multichannel quantum-defect treatment, in which a set of dressed channels corresponding to different photon numbers is defined, with intensity-dependent quantum defects and mixing angles. These quantities may be obtained by solving a system of close-coupling equations for the electron wave function, in a frame where the asymptotic electron oscillations are transformed away. This allows us to read off at a finite distance a radiative reaction matrix, which is a smooth function of energy for an energy range small compared with the photon frequency, and contains the net effect of radiative couplings. Calculations are presented for ionization of hydrogen s states in circularly polarized laser light, with allowance for above-threshold photon absorption.

Using linearly polarized synchrotron x rays with energies E=21.2–43.7 keV, differential cross sections for large-angle elastic photon scattering by Kr and Xe were measured. In the case of Xe, the energy region close to the K-shell binding energy ($B_K$=34.561 keV) was investigated in detail. The experimental results agree well with theoretical predictions based upon the numerical energy-shifted second-order S-matrix theory, and with high-energy-limit-corrected anomalous-scattering-factor predictions.

For a homogeneously broadened two-level system described by the optical Bloch equations, we show that the photon-absorption cross section σ(ω,‖A${\Vert }^2$) is not equal to the particle-excitation cross section σ’(ω,‖A${\Vert }^2$), where ω is the optical frequency and ‖A${\Vert }^2$ is proportional to the intensity. We detail how conservation of energy accounts for this inequality. Analytic expressions for these cross sections for weak intensities and strong intensities (to obtain the lowest-order Bloch-Siegert shifts for σ and σ’) are derived. We define an energy-loss cross section ${\sigma }_{\mathrm{loss}(\mathrm{\omega }}$,‖A${\Vert }^2$) for the bath responsible for the homogeneous broadening, and show that it is proportional to the change of the index of refraction due to the optical transition, Δn(ω,‖A${\Vert }^2$).

We present a unified theory of laser-induced autoionizinglike behavior in single-photon and multiphoton processes. We incorporate processes assumed unimportant in previous theories and on the basis of realistic calculations we interpret existing experimental results.

We present a general formalism of the theory of a three-level atom interacting with one-mode or two-mode cavity fields of arbitrary detunings. The dynamic behavior of the mean atomic level occupation probabilities are investigated numerically as functions of time and detuning parameters. A number of novel phenomena are discovered and discussed.

We study the interaction of a three-level atom with cavity fields of arbitrary detunings. We address ourselves in this paper to the question of how the time evolution of a coherent state depends upon the detunings. A number of interesting new phenomena contrary to the existing picture are found and discussed.

The power effects in the formation of stimulated photon echoes by broadband light pulses are examined both theoretically and experimentally. An angled-beam configuration is considered. Specific broadband features are expected to affect the signal intensity when the delay $t_{12}$ between the two first excitation pulses is varied across zero. The power dependence of these features is examined. In order to determine the expression of the signal intensity one has to solve the Bloch equation with random coefficients. Standard methods for solving stochastic differential equations are proved to fail when excitation is produced by delayed correlated pulses. A qualitative picture is proposed, which predicts the saturation decay of the signal as a function of $t_{12}$. Experimental recordings are in accordance with this conjecture.

A theory is presented of the Smith-Purcell diffraction radiation from a beam of point charges passing over a finitely conducting bigrating surface, with arbitrary orientation of the beam relative to the bigrating axes. The beam’s field can resonantly excite one or more surface-plasmon polaritons, which the bigrating can then decouple into a single outward radiating wave at any given angle and frequency. This radiation, arising from the collective motion of the electrons in a surface plasmon, has been shown theoretically to enhance the radiated power by two or three orders of magnitude in the peak direction. Numerical implementation of the present theory has shown that there is an optimal grating height at which this surface-plasmon-enhanced radiation peak is at a maximum. This work has also shown that a sinusoidal bigrating, forming a rectangular lattice, can yield an added enhancement, through two-plasmon excitation, when compared to the radiation from a classical grating (periodic in one direction).

We report on an experimental investigation of the collision kernels governing the effects of velocity-changing collisions, fine-structure-changing collisions, and their interplay, for Na–noble-gas pairs. The velocity distributions in the two Na excited-state fine-structure levels and in the Na ground-state hyperfine levels have been measured in the presence of a pump laser which produces velocity-selective excitation. For interpretation of these experiments we use a rate-equation model developed in the context of light-induced drift: the velocity-changing collisions are accounted for by a composite Keilson-Storer kernel describing large-angle and small-angle collisions and the fine-structure-changing collisions are treated in the sudden limit. The model is valid for arbitrarily high pump laser intensities and uses only a single adjustable parameter characterizing the small-angle scattering. It is found that the theory describes the experimental velocity distributions in all four Na levels over a wide range of experimental parameters for each Na–noble-gas pair. The relevance of the collision kernels deduced in the present work is discussed in the context of light-induced drift.

We examine the intensity fluctuations in the fluorescence from a single three-level atom exhibiting quantum jumps. The macroscopic intensity fluctuations revealed in the quantum random telegraph signal of emitted light are the signature of transitions between rapidly emitting and metastable states. We calculate the Mandel Q parameter for such a three-level atom both for incoherent and coherent driving and demonstrate how it provides a sensitive measure of the jumps. We show that the Q parameter reflects the existence of periods of brightness and darkness in the telegraph signal more directly than the second-order intensity correlation function.

An analysis is presented of optical heterodyne detection of an intracavity field within the context of quantum measurement theory. We find the intracavity density operator becomes diagonal in the basis which diagonalizes the measured quantity, a quadrature phase amplitude of the field. This representation is the ‘‘pointer basis,’’ and this result is the continuous-measurement equivalent of state reduction. The model illustrates a general feature of continuous measurement; one parameter given by the product of the system and measuring device coupling bandwidth and the fluctuations in the measuring device completely characterizes the measurement. This constant determines both the rate of diagonalization of the density operator and the rate of growth of fluctuations in the system quantity conjugate to the measured observable.

Helium atoms excited to an aligned (1s3d${)}^3$D state are produced by electron impact parallel to a magnetic field. The initial alignment of the atomic state evolves into an orientation with finite angular momentum along the magnetic field direction and thus gives rise to a circularly polarized component in the (1s3d${)}^3$D→(1s2p${)}^3$P radiation propagating parallel to the magnetic field. Circular-polarization fractions of a few percent are observed, in general agreement with theory. The measured polarization fraction is found to be pressure dependent, indicating that secondary excitation and cascade processes must be included for a complete description.

Using the Caldirola-Kanai Hamiltonian for the damped harmonic oscillator, exact coherent states are constructed. These new coherent states satisfy the properties which coherent states should generally have.

1${\omega }_0$ spectra from laser-produced plasmas have been observed at several angles to the backscattered direction with the use of very-large-F-number (F=25) collection optics. The spectra, produced by a single beam high-intensity ($I_0$${<10\mathrm{}}^{17}$ W/${\mathrm{cm}}^2$) Nd:glass laser incident on glass slab targets, are variously broadened, asymmetric, and red shifted with respect to the Doppler-shifted fundamental frequency, and display an irregular fine structure. These features are interpreted as due to the action of processes which modify the density profile and the expansion velocity of the critical surface, causing the phase of the outgoing light to vary nonlinearly in time. An analytic model is developed which shows that these features can be described primarily in terms of τ, the time scale for the phase modulation. The experimental results are compared with simulations using a one-dimensional computer code and reasonable agreement is obtained.

There is considerable evidence indicating that significant reduction in the efficiency of many processes in porous media, such as enhancing oil recovery, heterogeneous chemical reactions, deep-bed filtration, gel permeation, and liquid chromatography, is due to the reduction in the permeability of the pore space. This reduction is due to the transport of particles, whose sizes are comparable with those of the pores, and the subsequent blocking of the pores by various mechanisms. In this paper we develop a novel Monte Carlo method for theoretical modeling of this phenomenon. Particles of various sizes are injected into the medium, and their migration in the flow field is modeled by a random walk whose transition probability is proportional to the local pore fluxes. Pores are blocked and their flow capacity is reduced (or vanished) when large particles pass through them (and reduce their flow capacity) or totally block them. The permeability of the medium can ultimately vanish and, therefore, this phenomenon is a percolation process. Various quantities of interest such as the variations of the permeability with process time and the distribution of pore-plugging times are computed. The critical exponent characterizing the vanishing of the permeability near the percolation threshold appears to be different from that of percolation conductivity. The agreement between our results and the available experimental data is excellent.

Spatial distributions of light emission from electric discharges in ${\mathrm{N}}_2$ have been measured at very high electric-field–to–gas-density ratios E/n and low gas densities. The E/n range was from 270 Td to 107 kTd at gas densities from 1.3×${10}^{23}$ to 1.5×${10}^{21}$ ${\mathrm{m}}^{\mathrm{-}3}$ (1 Td≡${10}^{\mathrm{-}21}$ V ${\mathrm{m}}^2$). Planar electrodes and low discharge currents, less than 3×${10}^{\mathrm{-}4}$ A/${\mathrm{m}}^2$, insured that the electric field was spatially uniform. At the lower E/n and near the anode the intensities of first negative ${(1\mathrm{}}^{\mathrm{-}}$) and first ${(1\mathrm{}}^{+}$) and second ${(2\mathrm{}}^{+}$) positive bands of ${\mathrm{N}}_2$ increased exponentially with distance as expected from published measurements of the spatial growth of ionization. The first and second positive band intensities were placed on an absolute scale by normalization to previously measured or calculated excitation coefficients for E/n of 270 to 700 Td.

Because of the relatively weak signal at low E/n, the intensities of the first negative band at 391.4 nm are normalized to a theoretical value at extremely high E/n. At E/n above 4 to 30 kTd, depending on the transition observed, the emission peaked near the cathode. The ${\mathrm{N}}_2$ first negative band emission near 391.4 nm can be largely accounted for by direct electron excitation of the v=0 levels of $B^2$${\Sigma }_u^{+}$ state. Emission data from higher vibrational levels of the $B^2$${\Sigma }_u^{+}$ state at very high E/n are consistent with excitation of ${\mathrm{N}}_2$ by ${\mathrm{N}}_2$${\mathrm{}}^{+}$. The first and second positive band emissions appear to be the result of electron excitation only at the lower E/n and at positions near the anode. The emission of these bands near the cathode at the higher E/n is postulated to be the result of excitation of the ${\mathrm{N}}_2$ by about 100 eV molecules produced in charge-exchange collisions involving ${\mathrm{N}}_2$${\mathrm{}}^{+}$ ions moving toward the cathode. The required excitation cross sections are approximately ${10}^{\mathrm{-}20}$ ${\mathrm{m}}^2$ for the $B^3$${\Pi }_g$ group of states and ${10}^{\mathrm{-}21}$ ${\mathrm{m}}^2$ for the $C^3$${\Pi }_u$ (v=0) state.

Models of electron excitation and ionization at very high electric-field–to–gas-density ratios E/n are compared under conditions appropriate to discharge experiments at low gas densities, such as those in ${\mathrm{N}}_2$ described in the preceding paper. The models considered use the monoenergetic beam approximation in a velocity moment technique for solution of the electron Boltzmann equation. They differ in the treatment of the electrons produced by ionization and in the use of either the momentum balance or the energy balance to obtain the effective frictional effect. A simplified single-beam model is found to agree reasonably well with multiple-beam models, with the few published Monte Carlo results, and with experimentally measured spatial ionization coefficients.

For fluids in a periodic potential the grand-canonical potential per unit volume (negative ‘‘thermodynamic pressure’’) differs from the diagonal components of the average stress tensor. This is in contrast to homogeneous fluids. The thermodynamic meaning and the microscopic origin of this difference are discussed within the framework of classical statistical mechanics. For one-dimensional hard rods and for an ideal gas of diatomic molecules the two quantities are calculated exactly. General expressions are derived in a cluster expansion which can be applied to low-density classical fluids with more realistic interactions.