Six terms of the $4f^{14}5s^{2}5p^6\left({}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}\right)nl$ doublet system of Re vii have been found, including $nl=5d, 5f, 6s, 6p, 6d, \mathrm{and} 7s$. Thirteen spectral lines were classified in this system of levels. The partially resolved hfs of the $6s-sp$ multiplet was used to derive a value for the hyperfine splitting of the $6s$ level in agreement with a predicted value. The ionization energy of Re vii derived from the $\mathrm{ns}$ series is 82.74 ± 0.06 eV.

Measurement of proton kinetic-energy distributions from dissociative photoionization of ${\mathrm{H}}_2$ is reported, for incident-photon energies up to 41 eV. Data are presented for transitions involving the $1s{\sigma }_g$ ground state and higher states of ${\mathrm{H}}_2^{+}$. At a photon energy of 41 eV, direct ionization involving the $2p{\sigma }_u$ state accounts for approximately one-half of the dissociative ionization; other processes, autoionization or direct ionization involving states of higher energy than $2p{\sigma }_u$, account for the remainder.

Photoelectric spectra of the regions corresponding to resonance line emission of He-like ions of titanium, iron, and copper from a low-inductance vacuum spark were obtained, as were spectra of the regions corresponding to $K\alpha$ and $K\beta$ emission from the same elements and to $K\beta$ emission of molybdenum. Electron temperatures are estimated from continuous x-ray emission spectra to $\kappa T_e\lesssim 15$ keV; ion temperatures from x-ray line widths to $\kappa T_i\lesssim 10$ keV. A broad peak superimposed on the visible continuum is interpreted as anomalous bremsstrahlung at twice the electron plasma frequency. The resultant electron density is $N_e\approx 5\times {10}^{20}$ ${\mathrm{cm}}^{-3\mathrm{}}$, consistent with the absence of forbidden He-like ion lines. Experimental observations support the suggestion that the x-ray-producing dense plasmas are due to interactions between pulsed electron beams and low-temperature anode vapors or plasmas.

The acceleration, length, and velocity forms of the dipole operator are used to calculate the subshell photoionization cross sections in argon. First-order electron correlation corrections to the Hartree-Fock approximation are obtained through the use of many-body perturbation theory. For low-energy transitions the acceleration form of the operator is found to give very large errors in the Hartree-Fock approximation as compared to the length and velocity operators. Correlation effects for the three operator formulations are found to be quite different.

Space-charge amplification of the indirect ionization resulting from photoabsorption in cesium vapor has been shown to offer to conventional techniques of absorption spectroscopy a useful complement of highest sensitivity. It was used in this work together with a xenon continuum source filtered to a linewidth of 0.14 Å to measure the relative absorption probabilities for transitions of the cesium-principal-series ($6{}_{}{}^2{}_{}{}^{}S-n{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2},\frac{3}{2}}^{}{}_{}{}^{}$) doublets. Anomalous pressure effects on the resulting line-strength ratios, resulting in part from polarization molecules of ${\mathrm{Cs}}_2$*, were examined over a range of cesium-atom concentration varying from 1.2×${10}^{14}$ to 1.5×${10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$. From the corrected doublet line-strength ratios for $11\le n\le 16$, the segment of the curve of Fano $X$ parameters corresponding to discrete energies was constructed. Interpolation between these results and those from electron-polarization experiments served to locate the pole in the principal-series, doublet line-strength ratio near $19{}_{}{}^2{}_{}{}^{}P$.

A calculation of the double photoionization of neon using many-body perturbation theory has permitted a quantitative study of the relative importance of various contributing effects, i.e., ground-state correlations, inelastic internal collisions, core rearrangement, and a virtual Auger transition. The results are in good agreement with experimental data. The energy distribution between two outgoing electrons and the ratio of double to single photoionization are calculated and discussed.

The relative photoionization cross sections for cesium atoms selectively excited to the $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2},\frac{1}{2}}^{}{}_{}{}^{}$ states have been measured in a triple-crossed-beam experiment. A cesium discharge lamp produced resonant wavelengths of 8521 and 8944 Å for the excitation process. A Hg-Xe lamp combined with a grating monochromator was used for the actual ionization in the wavelength region from 2500 to 5000 Å. Background counts due to photoionization of ground-state cesium atoms and dimers as well as various surface effects were discriminated against by chopping the excitation light source. The data are compared with results from radiative-recombination measurements in which the fine-structure levels are not resolved and with recent model-potential calculations. The wavelength ($\lambda$) dependence of the cross section indicates a ${\lambda }^2$ dependence at threshold (≈ 5000 Å) and a ${\lambda }^4$ behavior at lower wavelengths.

The classical theory of dipole radiation is used to calculate the change in frequency of an electric-dipole-allowed transition due to the presence of a nearby reflecting surface. The result is compared to that for a perfect reflector.

Thermal beams of xenon atoms in single high Rydberg states have been produced by photoexcitation of $\mathrm{Xe}\left({}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}\right)$ metastable atoms. The highly excited states which were populated in this way were identified as $\mathrm{np}{\left[\frac{1}{2}\right]}_1$ with $11\le n\le 16$ and $\mathrm{nf}{\left[\frac{3}{2}\right]}_1$ with $8\le n\le 40$. The field ionization characteristics and radiative lifetimes of these atoms have been studied.

The ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}:{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ partial photoionization cross-section ratios have been measured for the rare gases in the ionization continuum and within resonance structure. The wavelength range for this study was from the ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ ionization threshold to 304 Å. The ratio of the cross sections was found to be constant over this wavelength range, yielding ratios of 1.54, 1.77, 1.93, and 2.18 for Xe, Kr, Ar, and Ne, respectively. Within resonances, the ratio changed dramatically. Results are illustrated for xenon.

We have measured all the fine-structure intervals in the configurations $1s7d$ and $1s7f$ of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ as well as the intervals $6{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}-6\mathrm{}{}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$ and $6{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}-6\mathrm{}{}_{}{}^3{}_{}{}^{}F_3^{}{}_{}{}^{}$ by a microwave-optical-resonance method. The level of accuracy considerably exceeds that of available calculations. We discuss the results in relation to the breakdown of $\mathrm{LS}$ coupling, and we estimate the singlettriplet mixing coefficients and the corresponding level perturbations. We obtain an improved fitting formula useful for predicting the frequencies of $n{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}-n{}_{}{}^{1,3}{}_{}{}^{}F_3^{}{}_{}{}^{}$ transitions.

A quantum-electrodynamic theory of spontaneous emission in presence of dielectrics and conductors is developed. The theory makes use of the master-equation techniques and the response-function formalism of part I of this series of papers. Various observable entities such as damping coefficients (lifetimes), Lamb shifts, and frequency shifts are related to the appropriate surface-dependent response functions. The results are valid for arbitrary geometries (involving linear dielectrics) and naturally contain, as a special case, the usual results of spontaneous emission in free space. As explicit examples we consider a two-level atom (also the multilevel atom) in presence of a plane dielectric interface and between two conducting plates. Formulas for the shifts and widths are given and their asymptotic behavior for large and short distances is discussed. The behavior when the atom is embedded inside the dielectric is different than when the atom is outside the dielectric. The origin of coherence in the present model is discussed and the coherence effects in this model are contrasted with those in Dicke's model. The results are also compared with those obtained by the image method. Exact expressions for the operator radiation-reaction fields are obtained in terms of the atomic polarization operators and response functions. Approximate results for such fields are also given. The far-zone behavior of the radiation fields is obtained in terms of response functions and the polarization operators. Some of the normally ordered correlation functions are also calculated. The connection of some of the theoretical results with a recent experimental work of Carniglia, Mandel, and Drexhage is discussed. The effect of anisotropy of the dielectric function on the lifetimes as well as on the far-field correlation functions is also considered. Finally the contribution to the shifts and widths due to the excitation of surface polariton modes is computed and the results are compared with those obtained by the quantization of surface polariton field. It is found that such surface modes contribute significantly to widths.

The method of high-temperature optical pumping has been used to measure the temperature dependence of the fractional hyperfine density shifts of ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$, ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$, and ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ in He, Ne, Ar, and ${\mathrm{N}}_2$ buffer gases over the temperature range 25-850°C. The first definite nonlinear temperature dependence has been found. All three alkali metals showed definite maxima in Ne, as did K and Rb in ${\mathrm{N}}_2$ and Na in Ar. In addition, Na in Ar has a zero density shift at 625 ± 25°C. Cubic and quartic polynomial fits of the density shifts versus $\frac{1}{\mathrm{kT}}$ have been calculated for each alkali metal and gas.

Higher conservation laws associated with the phase-dependent Maxwell-Bloch equations are derived and employed to determine both amplitudes and frequency shifts of the final-state solitons produced in a resonant medium by an initially phase-modulated optical pulse of area $<5\mathrm{}\pi$. The higher conservation laws are shown to provide a relatively efficient method of relating the parameters of the final pulses to those of the incident pulse. Connection is made to the computer work of Diels and Hahn.

We have considered the process of frequency conversion when the signal mode has an arbitrary field distribution. The set of coupled partial differential equations is solved employing the angular spectrum representation for the signal mode as well as for the idler mode. Explicit expressions for the signal and the idler field are obtained in the far-field approximation. An expression for the signal mode intensity is obtained which takes into account the effect of partial coherence as well as the effect of the bounded beam aperture. As an illustration we have considered the case of a Gaussian beam in detail.

Planckian thermal radiation of temperature $T$ shows a broad continuous spectrum and poor, monotonically decreasing, temporal coherence. We study the effects due to the discreteness of the exact resonances in a finite, cube-shaped cavity (volume $L^3$) bounded by perfectly reflecting walls. Using the Poisson summation technique, we calculate the almost periodic spatially averaged temporal ($t$) correlation tensors in terms of the simultaneous asymptotic series in powers of both $\frac{1}{\mathrm{LT}}$ and $\frac{t}{L}$ with Riemann and Epstein zeta-function coefficients. The according cross-spectral tensors yield all orders of the expansion of the spectral mode density including the oscillatory terms.

The quantum dynamics for two coupled harmonic oscillators is presented. Using the coupled-boson representation, the assumed problem is shown to be isomorphic with a perturbed angular-momentum oscillator. The current operator is obtained and its associated expectation values with respect to the number states, coherent states (Glauber states), and atomic coherent states are given. The eigenvalue spectrum of the current operator is seen to be finite and discrete. An interesting correspondence between this analysis and past work on Josephson tunneling and quantum interference is discussed.

We report on the effects of dense optical systems on the static and dynamic properties of laser light. The measurements of the angular irradiance distribution as a function of the optical density and the size of the scattering centers confirm previous measurements performed by Woodward. Our study of the scattered irradiance correlation function indicates that, in the presence of multiple scattering, the relaxation time may be significantly smaller than that predicted on the basis of the single-particle Brownian model. Furthermore, the angular dependence of the irradiance relaxation time deviates from the usual proportionality to the inverse square of the momentum transfer. We discuss a number of tests that have been performed to minimize the possibility that some of our conclusions could be affected in part by particle aggregation, surface charges, and depolarization of the scattered light.

We analyze the problem of a spin-½ system coupled to a longitudinal field $B_0$ and a transverse field $2Bcos\omega t$. We show that the magnetization is not periodic in general. Time-averaged population inversion is non-negative for the case $\omega =-\gamma B_0$. We discuss the significance of this result and show that eigenvalues of the Floquet Hamiltonian of Shirley's theory must be discontinuous at this point. The solution also exhibits satellite frequencies symmetrically displaced about odd multiples of $\omega$.

The evolution of slowly varying wave pulses in strongly dispersive and absorptive media is studied by a recursive method. It is shown that the resulting envelope function may be obtained by including correction terms of arbitrary dispersive and absorptive orders. Different definitions of pulse velocity are discussed in some detail and finally, qualitative examples of a Gaussian pulse in a cold plasma and an atomic medium are given, illustrating the importance of higher-order terms in the velocity expression. Particularly, the packet velocity is shown to be dependent on pulse width besides dispersion.