Partial doubly differential cross sections for multiple ionization $d^2$${\sigma }^{\left(n\right)}$/dE dΩ of argon, krypton, and xenon by electron impact have been measured as a function of incident electron energy and ejected electron energy, for argon up to ${\mathrm{Ar}}^{4+}$, for krypton up to ${\mathrm{Kr}}^{5+}$, and for xenon up to ${\mathrm{Xe}}^{8+}$. Incident electron energies between 0.5 and 10 keV were used, while the electrons ejected at an angle of 90° to the incident electron direction were detected with energies between 20 and 270 eV. The doubly differential cross section (sum of partial doubly differential cross sections) for ionization for each gas has been compared with experimental data in the literature.

Detailed calculations of the electron-impact excitation of the sodiumlike ion ${\mathrm{Al}}^{2+}$ were performed using both the unitarized Coulomb-Born approximation and the close-coupling approach. Calculations were undertaken at both the five-state (3s, 3p, 3d, 4s, and 4p) and nine-state (+4d¯, 4f¯, 5s¯, and 5p¯) levels of approximation. Calculations using Hamiltonians both with and without (semiempirical) core-polarization potentials were completed. Particular attention was paid to the resonance (3s-3p) excitation. The inclusion of core-polarization potentials resulted in cross sections for the resonance excitation that are 10% smaller in magnitude. As an additional check on the calculations, binding energies of ${\mathrm{Al}}^{+}$ bound states, and oscillator strengths for ${\mathrm{Al}}^{2+}$ transitions, were also computed and compared with the results of measurements and other calculations.

Scaling laws have been derived for total single-ionization cross sections from the classical picture of saddle-point ionization. The results agree with experimental data for the projectile-charge dependence of the energy position of cross-section maxima and for the values of the cross-section maxima.

The time evolution formula of state multipoles for states of hydrogenic ions in interaction with other ions is obtained in a rotating frame using an orthogonal-operator expansion. Our formula relates final-state multipoles to state multipoles of hydrogenic ions at earlier times. The theory is applied to the n=2 levels of hydrogen.

It is found that two simple dynamical relations can explain most observations of experiments on the orientation of the He 2${\mathrm{}}^1$P state induced by electron impact versus scattering angle in the process e(80 eV)+He 1 ${}_{}{}^1{}_{}{}^{}+\mathrm{H}\mathrm{e}$ 2 ${}_{}{}^1{}_{}{}^{}P$. In particular, by utilizing these relations and with the help of new quantum numbers, we identified a formula that can account for more than 80% of the orientation at large angles, which contains only three dynamical parameters of the form Im($S^{\mathrm{°}}$S) and one other, namely, the differential cross section at 180° scattering.

The spectrum of neonlike gold (+69) is observed in a beam-foil light source utilizing an x-ray crystal spectrograph. Precision wavelength determinations indicate variations from multi- configurational Dirac-Fock calculations for states sampling the 2s hole states consistent with previous observations in bismuth (+73).

Using both a bare-atom and dressed-atom picture of atom-field interactions, we present a theory of the pressure-induced resonances that can arise when four radiation fields interact with a three-level quantum system. The four fields drive two coupled atomic transitions which share a common level, the levels being arranged in a ‘‘ladder’’ scheme. As the field frequencies are varied, certain resonant structures in the excitation spectrum of the upper state population appear only in the presence of collisions. The resonant structures result from processes that have been referred to in the past as collisionally aided radiative excitation (CARE) and pressure-induced extra resonances in four-wave mixing (PIER4). We show that both CARE- and PIER4-type resonances have a common origin, which can be linked to conservation of energy. In contrast to conventional PIER4 signals, line shapes calculated in this work result from a ‘‘single atom’’ rather than a collective emission. Moreover, the signals vanish unless the applied fields are relatively coherent, again in contrast to conventional PIER4.

The magnetic moments of atomic nitrogen in the ${}_{}{}^4{}_{}{}^{}\mathrm{S}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{D}$ levels of its ground-state configuration are measured by microwave Zeeman absorption spectroscopy and compared to previous experimental and theoretical values. The values obtained for the corresponding $g_J$ factors are $g_J$${(}^4$$S_{3/2}$)=2.002 136 7(22), $g_J$${(}^2$$D_{5/2}$) =1.200 318 (5), and $g_J$${(}^2$$D_{3/2}$)=0.799 483 (15). The $g_J$${(}^4$$S_{3/2}$) value disagrees with the early experimental value obtained with the same technique but agrees with the more precise ones obtained by other techniques. The $g_J$${(}^2$$D_J$) values disagree significantly with the early experimental values previously known. The three $g_J$ values are found to be in agreement, to within a few ppm, with theoretical values obtained from detailed calculations within the Hartree-Fock self-consistent-field approximation.

Einstein transition probabilities for spontaneous emission within the ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ ground state of ${}_{}{}^3{}_{}{}^{}\mathrm{HeT}_{}^{+}{}_{}{}^{}$ have been calculated and an infrared fluorescence spectrum of ${}_{}{}^3{}_{}{}^{}\mathrm{HeT}_{}^{+}{}_{}{}^{}$ ions formed during β decay in molecular tritium is discussed.

Using fast-neutral-beam photofragment spectroscopy we have made a detailed analysis of the spectroscopy and dissociation dynamics of the triplet gerade n=3 Rydberg states in high (v>3) vibrational levels. Several hitherto unobserved levels have been found near the n=2 dissociation limit. The experimental energy levels are compared with an L-uncoupling model which is extended to include both nonadiabatic effects associated with the breakdown of the pure precession model and off-diagonal vibrational interactions. The kinetic energy and angular distribution of the fragments have been studied with translational spectroscopy using a time- and position-sensitive detector. The kinetic energy distribution not only confirms spectroscopic assignments but is also used to investigate structure in the excitation of the vibrational i ${}_{}{}^3{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ and $g^3$${\Sigma }_g^{+}$ continuum. Measurement of the angular distribution allowed us to determine the ratio for tunneling through the $i^3$${\Pi }_g$ and g ${}_{}{}^3{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ barriers for some v=4 levels. This showed that tunneling through the $i^3$${\Pi }_g$ barrier is the most efficient dissociation mechanism.

Computed lifetimes for the 4p ${}_{}{}^2{}_{}{}^{}P_{1/2}^{}{}_{}{}^{}$, 4$p^2$$P_{3/2}$, 4d ${}_{}{}^2{}_{}{}^{}D_{3/2}^{}{}_{}{}^{}$, and 4$d^2$$D_{5/2}$ levels in the copper isoelectronic sequence are presented for atomic numbers Z=29–92. These calculations agree well with recent high-precision lifetime measurements, conflict with the isoelectronic trend of single-configuration Dirac-Fock calculations, and agree at lower Z with the multiplet values of multiconfiguration Hartree-Fock calculations using experimental transition energies. Our calculations involve the inclusion of experimental energy-level data and the use of a Hartree-Slater potential to represent the ionic core. It is found that the core-polarization effects are significant and must be included to obtain agreement with experiment, at least for the lower members of the isoelectronic sequence. As part of the study, we have combined semiempirical parametrizations of the existing database with Dirac-Fock calculations to produce a set of values for the ionization potentials and the 4p and 4d excitation energies for all stable ions in this sequence.

Relativistic multiconfiguration Dirac-Fock (MCDF) calculations in the average-level (MCDF-AL) version with the inclusion of the transverse (Breit) interaction, self-energy, and vacuum polarization corrections have been carried out for molybdenum, palladium, lanthanum, and holmium to elucidate the structure of the Kα$L^n$ lines in their x-ray spectra. The examination of the effect of removing electrons from M shell on the principal Kα(Kα$L^0$) lines indicates that the most significant is the effect of removing 3p and then 3s subshells and that the effect of additional holes strongly increases with the atomic number. Detailed calculations have been performed on palladium to shed light on the structure of the Kα$L^n$ satellite lines of its x-ray spectrum, which is the first systematic theoretical study on the structure of these lines of a heavy atom. It has been found that in all cases the ‘‘average’’ positions of the groups of lines corresponding to the transitions of the type 1$s^{\mathrm{-}1}$2$p^{\mathrm{-}n}$→2$p^{\mathrm{-}(n+1)}$ obtained in the present work are very close to the recently measured experimental positions of appropriate Kα$L^n$ satellite lines. On the other hand, the structure of the satellite lines has been shown to be much more complex than can be observed experimentally. The results of this work can be used to construct different theoretical Kα$L^n$ spectra for palladium, satisfactorily reproducing the shape of various experimental spectra generated by different inducing projectiles.

The numerical multiconfiguration self-consistent-field method is used to calculate photoionization cross sections of atomic potassium in its ground state for photoelectron energies ranging from 0.0 to 12 eV. The effects of core polarization, which are very important for this atom, are analyzed in detail and are taken into account effectively ab initio in both the initial and the final state, by the configuration-interaction procedure. It is found that the core-polarization effect is very strong in the photoionization cross section of potassium. Our results are found to be in good agreement with previous theoretical calculations throughout the energy region considered and also with experiment except at high energies.

Many-body perturbation theory has been used to calculate photoionization cross sections with excitation of neutral argon from the single-ionization threshold at 15.76 to 100.00 eV. Resonance structure due to both single-electron excitations (3s→np) and double-electron excitations (3$s^2$3$p^6$→3$s^2$3$p^4$mn) has been included. Calculated cross sections leaving the ion in 3$s^2$3$p^5$, 3s3$p^6$, 3$s^2$3$p^4$${(}^1$D)md${(}^2$S), and 3$s^2$3$p^4$4p${(}^2$P) levels are compared with experiment and previous calculations. Calculated cross sections for 3$s^2$3$p^6$→3s3$p^6$εp and 3$s^2$3p→3$s^2$3$p^4$4pεd/εs excitations were used to determine the satellite intensities, which are compared with photoelectron measurements and other calculations. Results are also presented for the total cross section and the angular-asymmetry parameter for 3p electrons.

Hyperfine splittings in the 2$p_2$, 2$p_3$, 2$p_8$, and 2$p_9$ states of the 4$p^5$5p configuration of ${}_{}{}^{83}{}_{}{}^{}\mathrm{Kr}$ (I=9/2) have been measured using diode-laser optical pumping and saturated absorption spectroscopy. The resulting hyperfine coupling constants are in good agreement with calculated values.

The resonance fluorescence of a small sample of N two-level atoms driven by a strong resonant coherent field and damped by a squeezed vacuum is examined. The steady-state spectrum is shown to be dramatically dependent on the relative phase of the pumping field and on the squeezed-vacuum field in both the strong- and weak-squeezing limits.

We have measured the ratio of the fluorescence line intensities in the decay of a copper K-shell vacancy created in an inelastic-scattering event at intermediate momentum transfer. The measured value of the ratio of Kβ line intensity to Kα line intensity is 0.07±0.05, consistent with the value observed for excitation by photoabsorption. We also present data on the spectrum of x rays inelastically scattered from the copper K shell in a search for the predicted infrared divergence in the atomic scattering cross section. We find that the observed spectrum at low scattered x-ray energy in this and previous work is well described by secondary x rays produced in bremsstrahlung emission by photoelectrons.

The influence of the electron density gradients on the free-electron laser in the Raman regime is considered. Since in the Raman regime the electron density appears in the resonance parameter, the density gradients prevent the beam from being wholly resonant. The transverse gradients can then substantially reduce the gain even if the total current is kept constant. We solve a model problem of a free-electron laser, which employs a sheet electron beam in a planar wiggler, and which operates in the small-signal, high-gain regime. We study two cases, a density profile of uniform density gradient and a general density profile. For a uniform density gradient we write a dispersion relation explicitly in terms of Whittaker functions. For general density profiles, providing the current or the wiggler field is small, we derive an approximate dispersion relation through a solvability condition of the perturbed equations. In both cases, when the density gradient is large, the gain is expressed as a sum of contributions from the individual resonant layers, where each such contribution is inversely proportional to the density gradient at the respective resonant layer. A sufficient condition in order for the gain not to be substantially reduced by the density gradients is formulated.

We study the time evolution of SU(1,1) coherent states driven by a damped harmonic oscillator as described by the Kanai-Caldirola Hamiltonian. The coherence of these states is preserved and their time evolution is described by nonlinear ‘‘classical’’ equations. The trajectories of all SU(1,1) coherent states in phase space asymptotically approach a common point as t→∞. In all cases, this approach is accompanied by a damping of the associated energy expectation value to zero.

A photon-number quantum nondemolition (QND) measurement theory that takes dissipative losses into account is presented. A QND measurement criterion is developed to determine the feasibility of QND measurements in a lossy optical medium. Using an analysis based on loss-error characteristics, we examine a lossy Kerr medium. We obtain restrictions on the losses and requirements for the nonlinearity and signal and probe powers necessary to observe the QND effect. We calculate the expected results for an experimental system meeting such requirements. We conclude that QND measurements are possible in existing media.