The theory of prodistributions is applied to path integrate a general two-time quadratic action characterizing memory effects. The resulting Feynman propagator is exact and is in the form of an exponential integral over a single variable. A case where the integral is explicitly evaluated, for an arbitrary memory kernel, is presented to highlight the closed analytical structure of the propagator obtained. All special cases treated in the literature follow from this general expression.

The influence of excited states of the projectile on the charge states of relativistic heavy ions with Z<20 in solid targets is investigated. A four-state model for the dynamics of electron capture, ionization, and excitation of heavy ions by target atoms is formulated, and a simpler three-state model is solved analytically which explains gas-solid charge-state differences and metastable-state formation. Numerical calculations are compared with data of Crawford et al. for 140–2100-MeV/amu C, Ne, and Ar ions. The ionization, excitation, and radiative capture cross sections can be calculated accurately in this regime with use of the plane-wave Born approximation and the impulse approximation. Nonradiative capture cross sections are extracted from the data and are compared with theory.

A general formulation for thermal collisions between a Rydberg-state atom and a ground-state rare-gas atom is developed within the framework of the impulse approximation. This formulation allows calculation of cross sections for state-to-state transitions for an arbitrary initial orientation between the Rydberg-state atom and the relative velocity of the two partners of the collision. It also allows a direct computation of these cross sections averaged over all orientations, a situation corresponding to a cell experiment. In this formulation, the differential cross sections with respect to the modulus of the momentum transfer are obtained analytically in terms of rotation matrix elements. Numerical applications are made for the case of a sodium atom in a ‘‘circular’’ Rydberg state (‖n,l,m〉, with l=m=n-1) colliding with helium. The collisional processes are found to be highly anisotropic. In particular, a selection rule may appear, or disappear, depending upon the initial orientation. The extension to the case where an external electric field is present is also discussed, with special emphasis on symmetry properties.

Cross sections for single-electron capture by protons and single- and double-electron capture by helium ions from atomic lithium, sodium, and magnesium targets are presented. The absolute cross sections were measured by using the growth-curve method. Impact energies are in the range 2–100 kV q, where q is the projectile charge state. The present data are compared with previous experimental and theoretical work.

We have measured cross sections for formation of highly excited H (D) atoms in electron-detachment collisions of 2.8–60-keV/amu ${\mathrm{H}}^{\mathrm{-}}$ (${\mathrm{D}}^{\mathrm{-}}$) ions with H, ${\mathrm{H}}_2$, and Ar. The experimental technique employed a tungsten-tube furnace target and static electric field ionization. Excited hydrogen states with principal quantum number n between 12 and 28 were detected by measuring either the electrons or the protons resulting from field ionization. Electron detachment from ${\mathrm{H}}^{\mathrm{-}}$ is found to produce a 1/$n^3$ distribution of highly excited levels over the entire energy range studied. Comparisons with low-n data indicate that 1/$n^3$ scaling does not hold down to n=2 and n=3. The fraction of electron-detachment collisions that produce highly excited states has been measured as well. Above 20 keV the fraction is equal in ${\mathrm{H}}_2$ and H, yet the cross section for high excitation in ${\mathrm{H}}_2$ is twice as large as in H. This strongly suggests the validity of the independent-atom picture for ${\mathrm{H}}_2$ in these collisions above 20 keV. For direct comparison with electron capture, measurements have been performed with use of ${\mathrm{H}}^{+}$ projectiles. For ${\mathrm{H}}^{\mathrm{-}}$ collisions we have calculated the cross sections based on a simple high-energy model proposed by Drukarev which neglects electron correlation effects; poor agreement with experiment is found.

A method for including exchange exactly in the framework of the noniterative partial-differential-equation (PDE) approach [Phys. Rev. A 28, 621 (1983)] to electron-molecule scattering is presented. The method consists of breaking down the exchange equation into a set of inhomogeneous equations without integral terms. The difference form of the latter can then be solved by a straightforward generalization of the uncoupled noniterative PDE technique. Application is made to e-${\mathrm{N}}_2$ scattering in the fixed-nuclei approximation. The method is checked by comparing with other static- (exact) exchange calculations; agreement is found to be satisfactory particularly with new (unpublished) linear-algebraic results of Collins. A polarization potential, previously derived on the basis of a polarized-orbital treatment generalized to molecular targets, is then added; comparison is made with our previous results based on a Hara local exchange (HFEGE) approximation. The results show that HFEGE, as we had previously modified it, was less attractive than exact exchange. With exact exchange we are led alternatively to weaken the short-range part of the polarization potential with the consequence that agreement with other (exact) exchange-adiabatic calculations is excellent. The modified polarization potential is expected to be very useful in more elaborate scattering calculations.

Total attenuation cross sections have been measured for ${\mathrm{H}}^{+}$, ${\mathrm{H}}_2$${\mathrm{}}^{+}$, ${\mathrm{H}}_3$${\mathrm{}}^{+}$, and their deuterium analogs, and for ${\mathrm{N}}^{+}$ and ${\mathrm{N}}_2$${\mathrm{}}^{+}$ incident on a Cs target. The experimental conditions were arranged such that single-electron capture was the dominant attenuation mechanism. The energy range investigated for the hydrogen ions was 50–4000 eV, while that for the nitrogen ions was 350–4000 eV. The cross sections for the three hydrogen species were found to be large (≥${10}^{\mathrm{-}14}$ ${\mathrm{cm}}^2$) at all energies studied, while the cross sections for the nitrogen ions varied between 4×${10}^{\mathrm{-}15}$ ${\mathrm{cm}}^2$ at 350 eV and 1.5×${10}^{\mathrm{-}14}$ ${\mathrm{cm}}^2$ at 4000 eV. The cross sections for the molecular hydrogen ions are remarkable in that they remain essentially constant in magnitude down to the lowest energies studied. At the higher energies where comparison is possible, the present results agree with previous measurements.

A method has been derived for the evaluation of the Coulomb integral containing the product of a Coulomb wave function with a Slater-type orbital in a closed form. This method which is relevant to the charge transfer in second-order theories has been applied for the calculation of cross sections from the K shell of C, N, O, Ne, and Ar atoms by fast protons in the framework of the continuum intermediate-state approximation. The present calculated results are found to be in good agreement with the available experimental findings and the existing theoretical calculations in the high-energy region.

A distorted-wave model in its modified form (where distortion, polarization, and exchange effects as desired are appropriately implemented in both the channels) is used to calculate the differential and total cross sections for excitation of 2$p^2$ ${\mathrm{}}^3$$P_g$, 2p3p ${\mathrm{}}^1$$P_g$, and 2p3d ${}_{}{}^1{}_{}{}^{}$,3${\mathrm{D}}_{\mathrm{u}}$ states of neutral helium atom from the ground state 1$s^2$ ${\mathrm{}}^1$$S_g$. The results are compared with the available theoretical and experimental results.

We study collisional redistribution in the presence of two weakly exciting laser fields, including the effects due to degeneracy of the radiator states. A general expression for the total redistributed intensity is derived valid for arbitrary detunings and polarizations of the exciting laser fields. In particular, this expression contains all single- and sequential-collisional contributions, which are equally important under certain circumstances. We also point out the similarities and differences between the redistributed intensity as calculated in this paper and collisionally aided radiative excitation cross sections, which have been studied previously.

The effect of the autoionizing states 1s3l’nl, with n≥3 on the He-like effective excitation rates of ${}_{26}{}^{}{}_{}{}^{}$Fe xxv is examined. Results are obtained by computing directly the excitation rate coefficient for the processes 1$s^2$+e→1s3l’nl→1s2l’’+e, with n=3, 4, and 5, and by extrapolating them to n>5. For this ion, contribution of these autoionizing states to the excitation rate coefficients is more important than the corresponding contribution due to the 1s2l’nl autoionizing states. Nevertheless, the effect of all these resonances is much smaller than the effect of the radiative cascades.

We present calculations of the photoionization spectrum of excited hydrogen using π polarization in the presence of a strong electric field as a function of the spherical (applicable to complex atoms) and parabolic quantum numbers of the excited state. We also present corresponding measurements of the photoionization yield from the individual parabolic states of n=2. Both the calculations and the measurements show an enhancement of the depth of the so-called ‘‘Stark-induced modulation’’ in the region E≥0 when the initial excited state is a pure $m_l$=0 blue state, and disappear almost completely when the initial state is a pure $m_l$=0 red state. These results are understood using arguments based on the fact that the charge distribution of the Stark-induced states is tremendously extended up field. Because of the excellent signal to noise ratio of the enhanced modulations, we were able to measure the field dependence of the spacings with sufficient accuracy to confirm the (3/4) power law and rule out the recently suggested (2/3) power law.

The question of the temporal correlation of photons arising from a three-level atomic cascade is considered by calculating the joint probability of photoelectric detection for two detectors placed in the far field of the atomic emission. The analysis is carried out in the Heisenberg picture and involves the use of dipole, adiabatic (Weisskopf-Wigner), and rotating-wave approximations. Except for a small interval about zero time delay, which is however too short to be detected, it is found that the temporal correlation between emitted photons is one of sequential but otherwise statistically independent events, even when Landau’s generalized decay and frequency-shift terms are included. This result is compared with a well-known expression for the joint spectral density of the emitted photons.

The location of the zeros in dipole matrix elements for photoionizing transitions (Cooper minima) in ground states of atoms has been calculated for all subshells over the entire periodic system. These zeros occur for all subshells whose wave functions have nodes, except the 2s subshell. The behavior of these zeros, as a function of the atomic number Z, has been examined and their ‘‘trajectories’’ are rather complicated. The trajectories are explained primarily in terms of initial-state quantum defects and final-state phase shifts. All atoms with Z>10 have at least one zero, and some have as many as five zeros.

Calculations and measurements are presented of the increase in F¯=1 ground-state population as a function of incident laser intensity in optically pumped sodium. The calculations involve numerical integration of a multilevel version of the optical Bloch equations. Agreement between experiment and theory is good when proper account is taken of the residual Doppler width in the atomic beam, which causes a larger increase in the F¯=1 population. The F¯=1 population increases by 3.5% at 35 mW/${\mathrm{cm}}^2$, the highest laser intensity investigated.

Photoionization cross sections of neutral calcium with excitation to ${\mathrm{Ca}}^{+}$ 3d and 4p levels have been calculated from threshold to 50 eV by use of many-body perturbation theory. The cross section for leaving ${\mathrm{Ca}}^{+}$ in the 4s ground level is also presented in this energy range and compared with the 3d and 4p cross sections which at their thresholds are larger than the 4s cross section. All three cross sections show interesting structure near 31 eV due to the 3p→3d resonance.

A theory describing the interactions of an optically pumped target with an atomically polarizable buffer material is developed. Calculations indicate that a substantial increase in both target polarization and polarized target density can be achieved by using a polarizable buffer material. This target technique is potentially useful for optical pumping of buffer materials for which laser power is either insufficient or unavailable.

We report the measurement of Rabi oscillations in the optical pumping of a beam of metastable neon atoms in a three-level system with a cw dye laser. The laser beam is focused on the atomic beam, resulting in an interaction time with the laser beam of the order of the spontaneous lifetime of the induced transition. The Rabi oscillations are measured by a velocity-resolved analysis of the optically pumped metastable atoms. Adiabatic following is observed when the atoms cross the laser beam outside the waist, induced by the Doppler shifts due to the curvature of the wave fronts.

Steady-state stimulated Rayleigh-Brillouin gain spectroscopy and its application are reported. The stimulated gain, which is derived in terms of the spectral function of density fluctuations, is shown to approach, in the limit of zero density, the gain derived from the individual-particle picture of Rayleigh scattering. Using a pulsed pump laser, experimental gain spectra of pure ${\mathrm{SF}}_6$, pure Ar, and a ${\mathrm{SF}}_6$- and He-gas mixture are obtained and explained. Other associated coherent Rayleigh-Brillouin spectroscopies and the possibility of using a cw pump laser for higher spectral resolution are discussed.

This paper reformulates the problem of a dithered-ring-laser gyroscope as a mapping of points on the unit circle onto other such points. These mappings are represented by Cayley matrices. The relationship to our earlier Floquet theory is established, and it is shown how the properties of the mapping determine the lock-in behavior and the dynamics of the system. With square-wave dithering the mapping can be calculated analytically, and the expression allows rapid numerical exploration of the behavior in various regimes of operation. The Cayley transformation method is found to offer a convenient and intuitively transparent way to handle the locking phenomenon in a dithered ring laser.