The $L_2$-$L_3$ Coster-Kronig transition probability ($f_{23}$) in Tm was measured by multiparameter K versus L x-ray coincidence techniques. The Tm x rays were obtained from a radioactive source of ${}_{}{}^{169}{}_{}{}^{}\mathrm{Yb}$ and were detected with cooled germanium and silicon detectors of high-energy resolution. Corrections were applied for the contribution of K${\alpha }_1$ x rays to the K${\alpha }_2$ x-ray peak and for the contribution of unresolved Lη x rays to the L${\alpha }_1$,2 x-ray peak. The contribution of K${\alpha }_1$ x rays to the K${\alpha }_2$ x-ray peak was determined solely from the results of the coincidence measurements using a method of data analysis which was previously described elsewhere. The contribution of Lη x rays to the L${\alpha }_1$,2 x-ray peak was determined from the coincidence measurements and published values of the Lη to L${\beta }_1$ x-ray intensity ratio. The result obtained for $f_{23}$ is (13.44±0.24)×${10}^{\mathrm{-}2}$ or (14.06±0.24)×${10}^{\mathrm{-}2}$ depending on the value of the Lη to L${\beta }_1$ intensity ratio used in applying the correction. Both values are slightly lower than predicted by the latest theoretical calculations confirming a trend of departures from theory recently observed in other medium- and high-Z atoms.

Outgoing electron waves produced in the photodetachment of ${\mathrm{H}}^{\mathrm{-}}$ are propagated to large distances in a homogeneous electric field, and the electron flux is then computed. It is shown that the interference of waves propagating along two distinctive paths from the region of the bound state of ${\mathrm{H}}^{\mathrm{-}}$ to the same point induces oscillations in the electron flux distribution. Simple analytic expressions are presented for the flux distribution.

The properties of microwave diffraction by periodic dielectric media have been treated by extending the theory of dynamical scattering by perfect atomic crystals. The expressions of the form factor and of the structure factor have been obtained, and the conditions and limits of applicability of the two-wave approximation have been discussed. The diffraction pattern in Bragg geometry, the extinction length, the deviation from the Bragg law, and the width of the total reflection range have been evaluated for a two-dimensional periodic medium consisting of a regular array of cylindrical holes made on a polyethylene plane slab. We have reported the results of the experiment carried out to verify the accuracy of the theory. The comparison between theoretical and experimental results has shown good agreement.

Formal time-independent scattering theory is applied to multiphoton ionization of atoms in intense electromagnetic fields. The quantized-field version of the Volkov solution makes this approach possible. With the electron-photon interaction in a monochromatic photon field, it is found that, in the nonrelativistic and large-photon-number limits, the final scattering state exists only in the special case in which the ponderomotive potential per unit photon energy is an integer; otherwise the final state vanishes. In the integer case the corresponding wave function reduces to a single Volkov function, multiplied by an overlap factor. A simple interpretation of this result is given, and some other consequences of this work are discussed.

The many bands and continua of helium are reviewed, categorizing them by wavelength. Excited helium clusters dissociate, producing ultraviolet light. The population mechanisms of these molecules are deduced by using spectra, potentials, and the time evolution of excited atoms and molecules. Quartet ion recombination is proposed as accounting for the second decay component in low-energy afterglows. The roles of ${\mathrm{He}}_2^{+}$ and helium clusters are identified. Data available in the literature are used to calculate a lifetime of 0.55 nsec for the ‘‘metastable’’ state $A^1$${\Sigma }_u^{+}$ at 700 Torr. This lifetime gives a theoretical upper limit for the cross section for stimulated emission of 9×${10}^{\mathrm{-}18}$ ${\mathrm{cm}}^2$. The feasibility of a helium dimer laser that operates at 825 Å is assessed.

Calculations of the photoelectron angular distribution asymmetry parameter β for the excited 2$p^2$3p ${}_{}{}^2{}_{}{}^{}S$ state of atomic nitrogen have been performed using Hartree-Fock discrete and continuum wave functions with relaxation. The results show reasonably good agreement with a recent measurement of β at a single energy.

The 4$s_{1/2}$-4$p_{1/2}$ and 4$s_{1/2}$-4$p_{3/2}$ transitions in the Cu-like ions of the elements Sn, Xe, La, Nd, Eu, Gd, Dy, and Yb (atomic numbers Z=50, 54, 57, 60, 63, 64, 66, and 70) have been observed in the spectra from the Princeton Large Torus tokamak. The experimentally determined transition energies were compared to the transition energies calculated using the multiconfiguration Dirac-Fock technique. By including previously published observations, the experimental and calculated transition energies were compared for the entire Cu i isoelectronic sequence from Ru (Z=44) to U (Z=92). Contrary to the conclusion of Cheng and Wagner [Phys. Rev. A 36, 5435 (1987)], we find significant discrepancies between the experimental and calculated transition energies. The discrepancies are attributable to electron correlation corrections that are not accounted for in the calculation.

We have exploited the interference narrowing of Stark resonances to map electrostatic fields to a previously unattained level of accuracy and spatial resolution. The technique involves stepwise excitation with tightly focused laser light, an atomic beam, and temporal observation of ionization over a region of interference narrowing. Field inhomogeneities as small as 70 ppm have been detected with spatial resolution of 250 μm in three dimensions. The method is used here with rubidium atoms at fields of 3–4 kV/cm, but any alkali-metal atom over a range from a few tens of V/cm to a few tens of kV/cm is appropriate. Ionization rates may be calculated with the WKB quantum-defect method, but the field-mapping results are independent of the theory. Here this mapping technique is used to evaluate two electrode configurations for precision Stark spectroscopy. Field inhomogeneities produced by an electrode with a narrow slit, when properly constructed, are found to be in good agreement with detailed electrostatic calculations. However, discrepancies between field measurements and calculations for a metal mesh over an aperture indicate the presence of unavoidable crinkles of the mesh. We conclude that the slot is the preferred arrangement, and we present calculations that give the field inhomogeneity as a function of the slot size.

An experiment is described in which a coherent superposition of the Rydberg states of atomic potassium is excited by a short optical pulse. The coherent superposition forms a wave packet localized in the radial coordinate. The radial motion of the wave packet is periodic with the period of the classical Kepler orbit. The time evolution is probed by a second short pulse. The resulting photoionization signal, as a function of the delay between pulses, shows the classical periodicity.

Two independently tunable, linearly polarized dye lasers are counterpropagated through a heat pipe containing sodium vapor. The frequency of the first laser ${\omega }_1$ is incremented through both 3$p^2$$P_{1/2}$,3/2 fine-structure levels while the second laser ${\omega }_2$ is scanned through the energy increment necessary to reach ns ${}_{}{}^2{}_{}{}^{}S_{1/2}^{}{}_{}{}^{}$ and ${\mathrm{nd}}^2$$D_{3/2}$,5/2 levels (n=5–35). Following excitation, ionization occurs through chemi-ionizing collisions. The polarization (defined as the ionization intensity measured when the two planes of polarization of the laser beams are parallel minus the intensity when perpendicular divided by the sum of the intensities) P=($I_{?}$-$I_{\perp }$)/($I_{?}$+$I_{\perp }$) goes from +1 to -1 as ${\omega }_1$ is tuned between the 3$p^2$$P_{1/2}$,3/2 fine-structure levels. This novel polarization effect is shown to be due to an interference between the two pathways to the ns ${}_{}{}^2{}_{}{}^{}S_{1/2}^{}{}_{}{}^{}$ levels. Upon exciting the unresolved nd ${}_{}{}^2{}_{}{}^{}D_{3/2}^{}{}_{}{}^{}$,5/2 levels, the polarization is very close to zero when ${\omega }_1$ is at or near the 3p ${}_{}{}^2{}_{}{}^{}P_{3/2}^{}{}_{}{}^{}$,1/2 levels. A simple few-level atom theory reproduces the experimental observations except for the case when both lasers are in resonance.

Calculations of the Stark scalar and tensor polarizabilities ${\alpha }_0$ and ${\alpha }_2$ for the 6$P_{3/2}$ state in cesium are reported, along with values of ${\alpha }_0$ for the 6$S_{1/2}$, 7$S_{1/2}$, and 6$P_{1/2}$ states. The results are in very good agreement with the latest measurements. We also used our method to calculate the Stark amplitude coefficients for the 6$S_{1/2}$-7$S_{1/2}$ transition; the results are compared with those of previous theoretical and experimental work.

Partial photoionization cross sections and angular distribution asymmetry parameters for atomic xenon have been calculated in the relativistic random-phase approximation for 26 jj-coupled channels over a wide range of energies (0–1 keV). The effects of relaxation on the 4d and 3d cross sections are examined by using a modification of the relativistic random-phase approximation that calculates excited-state orbitals in the potential of the relaxed ion. Results are compared with Hartree-Fock theory, with the nonrelativistic random-phase approximation, and with recent photoemission experiments.

The three-dimensional optical pattern generated in a single pulse by a high-power free-electron-laser system when the $e^{\mathrm{-}}$-beam radius is small compared to the laser-beam radius is shown to be determined by the solution of a simple one-dimensional integral equation. This strong-diffraction-limit equation is of the convolution form and, while it is mostly easily solved numerically, it is shown to have nontrivial analytic solutions of interest.

The effects of cross-phase modulation (XPM) on the evolution of copropagating ultrashort pulses in an optical fiber are discussed theoretically by solving the coupled-amplitude equations which include the contributions of self-phase modulation, XPM, pulse walk-off, and group-velocity dispersion. A pump-probe configuration is studied to isolate the XPM effects. In the case of nondispersive XPM, the probe shape remians nearly unchanged while the probe spectrum exhibits asymmetric spectral broadening and a shift toward the red or the blue side depending on the initial pump-probe delay. In the case of dispersive XPM, the combination of group-velocity dispersion and XPM lead to both temporal and spectral changes. The new XPM-induced phenomena, optical wave breaking, and pulse compression are discussed in detail.

We discuss in detail the influence that the statistical properties of the pump source have on maser and laser dynamics. We derive a general master equation for the radiation field that is valid for a wide range of different pump mechanisms. If the pump noise is eliminated, we find that the photon number noise in a micromaser and a laser can be significantly reduced below the shot-noise level. In contrast, the phase fluctuations for both maser and laser are unaffected by the noise contribution of the pump.

Optical guiding in a Raman free-electron laser (FEL) is studied theoretically and experimentally. Two complimentary theoretical approaches to the problem of optical guiding in a waveguide containing a filamentary electron beam are given and shown to be in good agreement with each other in the exponential gain regime. Evidence for optical guiding of 2-mm-wavelength radiation along the electron beam in the Columbia University FEL is obtained experimentally by analysis of spatial ‘‘ring-down’’ data of the optical wave profile and compared with numerical simulations. These data are presented for the exponential gain regime. A similar experiment at signal saturation conditions shows a much less well-defined ring-down. We give plausible experimental as well as theoretical arguments why the ring-down pattern is less well defined. Based on the observations presented in this paper, it is not possible to validate optical guiding at saturation.

An algebraic scheme for the perturbative calculation of resonant optical susceptibilities is presented that explicitly includes resonant population of multiple excited states as well as arbitrarily complex feeding between states. The scheme is derived through a novel analytic matrix inversion of the Liouville equation within the rotating-wave approximation, thus eliminating the need for numerical matrix inversions of order $N^2$ for N-level systems. Simple analytic solutions may be obtained by a diagrammatic analysis. This approach is valid both for closed systems and for systems in which the optically active states are coupled through feeding to an infinite bath of dark states. By rigorously including realistic population dynamics, this method also avoids the problem of divergent solutions for states of infinite lifetime. Expressions for resonant emission are derived, which show that feeding (particularly reversible feeding) can alter the interference between the fluorescence and Raman terms of the susceptibility, leading to new resonances similar to those associated with pure dephasing. This effective source of dephasing, however, cannot be described by an enhanced off-diagonal (dephasing) relaxation rate.

We report an experimental study of one- and two-photon Rabi oscillations and other coherent effects in microwave transitions between Rydberg states of calcium. Selective field ionization allows us to observe the time evolution of both the initial and final states with high discrimination. The experiments include measurements of the dependence of the one- and two-photon oscillation frequencies on microwave power and detuning from resonance. We have used the off-resonant behavior of the two-photon oscillation frequency to measure the ac Stark shift. In a magnetic field we have also observed the free evolution of the magnetic sublevels and the effect of Zeeman splitting on the one-photon Rabi oscillations. The theory for these experiments is presented; our results are in excellent agreement.

A generalized Jaynes-Cummings model is investigated where the transition is mediated by two different modes of photons. For different types (uncorrelated and correlated) of field states, the dynamical behavior of the generalized Jaynes-Cummings model exhibits very different aspects. With the high-Q limit, the effects of cavity damping in the presence of correlated field states are also considered.

For a system of an M-level atom interacting with cavity fields, the statistical properties of the field are investigated numerically. The variation of photon antibunching and probability distribution with the atomic level number and initial field intensity is discussed for both resonance and off-resonance cases.