High-resolution Auger spectra of doubly excited Be-like neon have been obtained for intermediate collisional velocities (0.89–1.79 a.u.). ${\mathrm{Ne}}^{8+}$ was produced at high voltage in the Argonne National Laboratory electron-cyclotron-resonance ion source. A differentially pumped helium gas cell was used to study double electron capture. The LMX Auger decays of the Be-like neon are observed with a high-resolution 0° tandem electron spectrometer. High-angular-momentum states are observed to be populated during the collisions and their relative amplitudes change dramatically with increasing collisional velocity.

Double-electron-capture cross sections to individual doubly excited states and autoionizing electron spectra at fixed angles for ${\mathrm{Ne}}^{8+}$-He collisions are calculated and analyzed for collision energies from 20 to 80 keV/amu. An independent-electron approximation is adopted where the amplitudes for double capture are derived from the antisymmetrized product of single-electron-capture amplitudes properly weighted with configuration-interaction coefficients. By choosing the quantization axis to be perpendicular to the collision plane, we also study the propensity rule for the M distribution of the cross section for each doubly excited state. The electron spectra at 0° are compared with experiments. At 80 keV/amu collision energy, our theoretical spectrum agrees with experiment very well. At lower energies, the agreements are not as good, but the dominant features are well predicted.

External-bremsstrahlung spectra excited by soft β particles of ${}_{}{}^{147}{}_{}{}^{}\mathrm{Pm}$ (${\mathit{E}}_{\mathrm{\beta }}^{\max }$=225 keV) and ${}_{}{}^{35}{}_{}{}^{}\mathrm{S}$ (${\mathit{E}}_{\mathrm{\beta }}^{\max }$=167 keV) in targets of Al, Cu, Sn, and Pb have been studied. The experimental and theoretical results are compared in terms of the number of photons of energy k per ${\mathit{m}}_0$${\mathit{c}}^2$ per unit photon yield to exclude the uncertainty in the source strength measurement and overcome the inherent inadequacy of the normalization procedure used by earlier workers. The results of present measurements for medium- and high-Z elements show better agreement with the theory of Tseng and Pratt [Phys. Rev. A 3, 1714 (1976)] than with Elwert’s corrections [Ann. Phys. (N.Y.) 34, 78 (1939)] to the Bethe-Heitler theory [Proc. R. Soc. London Ser. A 14, 83 (1934)], particularly at the higher-energy ends. However, for low-Z elements, both theories are found to be adequate.

The W value, or the average energy required to produce an electron-ion pair, was measured in liquid krypton with a pulsed ionization chamber and ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ 976-keV internal-conversion electrons. From the charge collected at the highest electric field of 16 kV/cm, the W value was determined to be 18.4±0.3 eV. Extrapolation of the charge to infinite field strength yields a smaller W value, reduced by an amount which depends on the recombination model used to fit the data. The δ-electron model gives the lowest value of 16.8 eV. An estimation of the W value in liquid krypton, using Platzman’s energy-balance equation, is in good agreement with the experimental result, but is not precise enough to rule out model-dependent lower values.

The use of the multiparameter generalized reduced-potential-curve (GRPC) method proposed in a previous article [F. Jenč, Phys. Rev. A 42, 403 (1990)] is tested on a group of eight alkali-metal diatomic molecules (for which the value of the depth of the minimum of the potential, ${\mathit{D}}_{\mathit{e}}$, and the potential up to the dissociation limit are known) in extending their ground-state potential from 45% up to the dissociation limit. For the repulsive limb, the one-parameter (α) GRPC approximation is satisfactory. Error limits of only 1–6 ${\mathrm{cm}}^{\mathrm{-}1}$ in energy for the attractive limb and less than 0.002 Å in the internuclear distance for the repulsive limb are obtained. The method may be used for an accurate prediction of the upper portion of the potentials (and the spectrum) of the remaining seven alkali-metal diatomic molecules where the molecular spectrum has not been measured [F. Jenč and B. A. Brandt, J. Mol. Spectrosc. 154, 226 (1992)].

A systematic investigation of double-electron KL-edge resonances in x-ray-absorption spectra of third-period atoms (Si, P, S, and Cl) is presented. Experimental data on ${\mathrm{NaH}}_2$${\mathrm{PO}}_4$, Graham’s salts (${\mathrm{Na}}_2$O:${\mathrm{P}}_2$${\mathrm{O}}_5$), ${\mathrm{Na}}_4$${\mathrm{P}}_2$${\mathrm{O}}_7$, elemental S, ${\mathrm{Na}}_2$${\mathrm{SO}}_3$, ${\mathrm{K}}_2$${\mathrm{SO}}_4$, ${\mathrm{CuSO}}_4$, ${\mathrm{Na}}_2$${\mathrm{S}}_2$${\mathrm{O}}_3$, ${\mathrm{Na}}_2$${\mathrm{S}}_2$${\mathrm{O}}_6$, ${\mathrm{NaClO}}_2$, ${\mathrm{NaClO}}_3$, and ${\mathrm{NH}}_4$${\mathrm{ClO}}_4$ are reported and discussed in combination with previous measurements at the Si KL edge of Si${\mathit{X}}_4$, (X=H,${\mathrm{CH}}_3$,Br,Cl,F) molecules. The further comparison of these results with KL-edge structures in Ne and Ar provides an almost complete overview of these excitations for third-period atoms. A compilation of energies and oscillator strengths for the dominant resonances is reported and the main trends of energy splitting, intensity, and energy position versus oxidation state and Z number are discussed.

By computer-simulation and analytic studies for binding energies and microscopic shell structures, it is shown that Coulomb clusters assume particularly stable configurations at certain ‘‘magic numbers’’ of particles. Through analyses with the spherical Voronoi numbers, a special role that the icosahedral geometry plays in shaping the particle configurations on the spherical surfaces is elucidated. Gross features in the cluster structures, such as the shell radii and intershell partition of particles, are well accounted for by an appropriate shell model.

Aligned atomic Rydberg states of sodium can be prepared using two-step excitation from the ground state by linearly polarized pulsed lasers. Information that is normally inaccessible, e.g., sublevel partial cross sections in charge-transfer experiments, can be obtained when aligned targets are used. The calculations of orbital alignment must carefully allow for fine and hyperfine structure, laser linewidths, pulse widths and delays, sublevel coherences, and other factors. In this paper we derive the orbital alignments and time-averaged d-state sublevel populations for 3 ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2}$→3 ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{\mathit{J}1}$→n ${}_{}{}^2{}_{}{}^{}$D excitations in Na using angular-momentum and density-matrix methods. We consider both quadrupole alignment ${\mathit{A}}^{\mathrm{}\left(2\right)\mathrm{}}$ and hexadecapole alignment ${\mathit{A}}^{\mathrm{}\left(4\right)\mathrm{}}$, with excitation through either ${\mathit{J}}_1$=1/2 or 3/2 intermediate states considered on the same footing. We show sublevel populations for ‖${\mathit{M}}_{\mathit{L}}$‖=0, 1, and 2 analytically and graphically. Finally, we formulate the experimental design problem quantitatively in order to ascertain how to optimize the choice of polarizer angles for extraction of sublevel partial cross sections. Although perhaps the commonest instance, two-step excitation of Na(nd) is but one of a large number of interesting cases, and this study is further intended to illustrate and guide the application of these methods to other light atoms.

The comparison of kinetic-energy distributions and ionic fragment yields produced from ${\mathrm{CO}}_2$ and ${\mathrm{N}}_2$O in fast-ion collisions and multiphoton ionization reveals three comparative and distinguishing features of the interactions. They are (i) similarities in the ${\mathrm{O}}^{\mathit{q}+}$ (specifically ${\mathrm{O}}^{3+}$) energy distributions from ${\mathrm{CO}}_2$ arising from correspondingly similar magnitudes of the peak electric fields occurring in the interactions, (ii) a strongly dissimilar pattern of site-dependent ionization as observed in ${\mathrm{N}}_2$O, and (iii) a marked similarity in the production of anomalously energetic ${\mathrm{C}}^{2+}$ ions arising from high-lying ${\mathrm{CO}}^{2+}$ precursors having a substantial charge-transfer character.

We constructed an optical Ramsey atomic interferometer, which has a resolution of 8 fm for the difference between arms of the interferometer, and used it to examine the phase shift due to the ac Stark effect of the excited state of the intercombination line ${(}^1$${\mathit{S}}_0$${\mathrm{-}}^3$${\mathit{P}}_1$) of Ca. It was clearly observed that the phase shift is in proportion to the field power and in inverse proportion to the detuning frequency of the laser. The proportionality coefficient obtained was in good agreement with the theoretical one.

We present experimental and theoretical investigations of a Gaussian laser beam interacting with Zeeman-tuned J=1→J=0 atomic systems. In our experiment a single-mode cw dye-laser beam traverses a neon discharge in a longitudinal magnetic field. The excited neon transitions used for these studies are 1${\mathit{s}}_4$(J=1,g=1.464)→2${\mathit{p}}_3$(J=0) and 1${\mathit{s}}_2$(J=1,g=1.034)→2${\mathit{p}}_1$(J=0). In the laser-induced forward-scattered light, dark and bright ring-shaped structures are observed. The ring structures are investigated as a function of the magnetic detuning of the m=±1 sublevels and as a function of the laser-beam power. We find that the line shapes of the spectra, i.e., the forward-scattered light intensities as a function of the magnetic detuning, are sensitive to the transverse intensity distribution of the laser beam. Analytical expressions based on a semiclassical theory are derived and the calculated results on the ring structures and the spectra are compared with the experimental results. Good agreement between the calculated and the experimental results are obtained only when the transverse effects are taken into account.

We present a detailed theoretical investigation of the absorption spectrum of a probe beam after transmission through a one-dimensional optical molasses obtained with circularly cross-polarized counterpropagating pump beams (corkscrew molasses). The study is performed for a ${\mathit{J}}_{\mathit{g}}$=1→${\mathit{J}}_{\mathit{e}}$=2 atomic transition and the external degrees of freedom are described by means of a Fokker-Planck equation in the regime where the stationary momentum distribution lies within the range of linearity of the cooling force. We analyze the stimulated Raman transitions occurring between differently populated and light-shifted ground-state Zeeman sublevels. In the case where the probe beam has the same polarization as the copropagating cooling beam, an additional narrow Rayleigh resonance appears for a probe frequency close to the pump frequency. Its width is equal to 2α/M, where α is the friction coefficient of the cooling force and M is the atomic mass. In the case where the probe beam has the same polarization as the counterpropagating cooling beam, a central recoil-induced resonance is expected. Its width is related to the Doppler width of the optical molasses.

We investigate the population trapping in a Raman-coupled three-level system interacting with a pump mode and a Stokes mode in a quantized cavity. We show that with an initial atom-field decoupled state and the atomic state prepared in a coherent superposition of two nondegenerate ground states, population trapping occurs when the phase of the atomic dipole is equal to the phase difference of the two modes and the two-mode field state satisfies a specific photon distribution. In the limit of large total photon number, under some specific conditions, the corresponding two-mode trapping state can be identified as a phase difference state. We have studied the variance of superposition mode quadrature and its evolution, statistical properties, and the phase-space properties of the two-mode trapping field state. It has been observed that although under different conditions the two-mode field exhibits both sub- and super-Poissonian statistics, no squeezing is observed in any case.

We extend the theory of velocity-selective laser optical pumping in atomic vapors, allowing for arbitrarily rapid velocity-changing collisional rates. The results yield a simple relationship between the line-shape areas of narrow spectroscopic features present in optically pumped samples. This relationship gives directly the ground- and excited-state velocity-changing collision rates and cross sections. We use the results to analyze the data from a laser optical-pumping experiment in ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ vapor perturbed by Ar buffer gas.

Laser cooling based on velocity-selective coherent population trapping is investigated theoretically. Quasiclassical treatment is used to identify the conditions for optimal cooling and to study the dynamics of the cooling process in detail. For different cooling schemes we give the analytical expressions for the temperature of the cold atoms, which can be much lower than the Doppler cooling limit. The effect of the degree of incompleteness of coherent population trapping on dynamics and the limits of laser cooling are revealed.

We present a coupled-channel study of optical collisions, restricted to a single atom-laser manifold. Outside of a resonance region around the Condon point, we find a simple representation of the solution in terms of propagating complex dressed states. The probability flux for the ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{3/2}$+S state at small interatomic distances can be interpreted in terms of two such interfering dressed states. The coupled-channel solution displays some features that have previously been obtained with semiclassical optical-Bloch-equation methods. An important quantum effect, however, is a strong reduction of atom loss rates at low collision energies that is roughly proportional to ${\mathit{E}}^{\mathrm{-}2}$.

Laser cooling of a single trapped ion with Zeeman substructure below the Doppler limit is considered theoretically. The laser field consists of two counterpropagating beams linearly polarized in different directions, and the internal atomic transition is ${\mathit{J}}_{\mathit{g}}$=1/2→${\mathit{J}}_{\mathit{e}}$=3/2. The ion is assumed to be localized to spatial dimensions smaller than the optical wavelength (Lamb-Dicke limit) and placed at a specific position with respect to the laser beams. Under the assumption that the rate for optical pumping between the atomic ground states defines the smallest time constant in the system, analytic expressions for the final energy and the cooling rates are derived, with both a semiclassical and a full quantum treatment. The results show that laser cooling of a trapped ion using polarization gradients leads to very low energies. These energies are insensitive to the precise localization of the ion with respect to the lasers, the angle between the direction of the polarizations of the laser beams, and the detuning of the cooling laser.

The billiard-ball model (BBM) is redeveloped to allow quantitative diagrammatic evaluation of signal parameters associated with optical coherent transient experiments. It is expanded to include the action of external forces and fields as well as to include atomic-beam-type experiments. Matter-wave interferometric experiments are examined in the context of the BBM and their relationship to photon-echo experiments is explored.

We study transmitted optical spectra from a realistic system which consists of a degenerate optical parametric oscillator (DOPO) and N two-level atoms. Optical bistability appears when parameters are suitable. Below the modified threshold of the DOPO (lower turning point of the bistable curve), the coherent intensity is always zero at the lower branch, which allows us to describe this system with a set of linear differential equations. By transforming the field and atomic variables into corresponding quadratures, we find that, for the resonance case, one atomic quadrature will only couple to one field quadrature. By separating these two quadratures, we are able to study the effects due to squeezed and unsqueezed quadratures on the atoms. The optical and atomic spectra of this system are obtained, analytically, for arbitrary coupling strength and cavity linewidth.

The influence of light polarization on the dynamics of an optically pumped single-mode laser with a homogeneously broadened four-level medium is theoretically investigated in detail. Pump and laser fields with either parallel or crossed linear polarizations are considered, as are typical in far-infrared-laser experiments. Numerical simulations reveal dramatically different dynamic behaviors for these two polarization configurations. The analysis of the model equations allows us to find the physical origin of both behaviors. In particular, the crossed-polarization configuration is shown to be effective in decoupling the pump and laser fields, thus allowing for the appearance of Lorenz-type dynamics.