Using the resonance-enhanced multiphoton-ionization technique, we have identified the n ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{1/2}^{}{}_{}{}^{}$(7≤n≤20), ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{3/2}^{}{}_{}{}^{}$(7≤n≤23), and ${}_{}{}^2{}_{}{}^{}\mathrm{F}_{5/2,7/2}^{}{}_{}{}^{}$(5≤n≤21) Rydberg states following photodissociation of TlI. The ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{1/2,3/2}^{}{}_{}{}^{}$ spin-orbit splitting can be resolved and well compared to its theoretical counterpart with an accuracy of ±3.5%. In terms of photoionization-cross-section prediction, we have also satisfactorily interpreted the discrepancy for the relative ionization intensity, via the respective intermediate ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{3/2}^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{1/2}^{}{}_{}{}^{}$(n≤11) doublets, from their statistical weight.

We observe optical phase conjugation using the surface nonlinearity of a dense atomic potassium vapor. For an atomic number density of 1.5×${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$, phase-conjugate reflectivities of 4×${10}^{\mathrm{-}5}$ are measured for pump intensities approaching the saturation intensity of 10 W ${\mathrm{cm}}^{\mathrm{-}2}$. We also demonstrate aberration correction using surface phase conjugation. The measured properties of the surface-phase-conjugate signal are in excellent agreement with the predictions of a theory of surface phase conjugation by degenerate four-wave mixing, in which the origin of the nonlinear response is saturated absorption.

We present a nonperturbative result for the spectrum of spontaneous photons emitted by an atom coupled on resonance to a standing-wave cavity mode. Motion of the atom through the standing-wave mode function is included in a classical way. We discuss the form of the spectrum as a function of the velocity of the atom in the limit of strong dipole coupling. For slow atoms the normal-mode doublet (‘‘vacuum’’ Rabi spectrum) survives with small changes. The motion of a fast atom through the standing wave averages the coupling constant to zero, and the spectrum reverts to a single peak. At intermediate velocities the spectrum has a complicated multipeaked structure that can be understood in terms of interfering probability amplitudes for different quantum-mechanical emission paths or as a frequency-modulation spectrum for radiating coupled oscillators.

Femtosecond-pulse propagation in resonantly excited semiconductors is investigated by numerically solving the semiconductor Maxwell-Bloch equations for plane waves. For excitation at the exciton resonance, it is shown that the pulse absorption exhibits a strongly nonlinear dependence on the input pulse area. Very long propagation distances for strong pulses are observed, but even when all dephasing processes have been neglected, no lossless propagation (self-induced transparency) was found. The influence of the electron-hole many-body effects, nonequilibrium carrier relaxation, and optical dephasing on the pulse-propagation dynamics is studied. The exchange interaction in the electron-hole plasma is shown to support large propagation distances. For excitation of the continuum states, the dependence of the absorption on the intensity of the input pulse is reduced due to the rapid carrier relaxation into quasiequilibrium distributions.

The superposition states from several two-mode coherent states are studied. It is shown that under certain conditions the superposition states may exhibit nonclassical effects, such as two-mode squeezing, violation of the Cauchy-Schwartz inequality, and sub-Poissonian statistics.

We present an alternative cavity QED model with three nondegenerate quantized field modes. The atom-field interaction is a cavity analog of Raman scattering, and the three field modes can be associated with pump, Stokes, and anti-Stokes frequencies. Unlike systems based on the Jaynes-Cummings model, this one has two independent channels connecting the two active atomic levels, leading to the possibility of quantum interferences. Despite its complexity, the model has eigenstates and eigenvalues that can be found exactly and fully analytically in finite terms. The most interesting eigenstates have a ‘‘chain’’ character unknown in previous cavity QED models. Both Fock-state and coherent-state solutions are presented for a number of quantities, including complex three-mode variables. Heisenberg operator solutions are demonstrated in a few cases, and an example of fourth-order quantum interferences due to the coupled channels is worked out in full.

Nonlinear effects of sublevel coherence on resonant backward-degenerate four-wave mixing are analyzed in the saturation regime of an inhomogeneously broadened and optically thin gas medium, composed of Λ-type three-level atoms. No limitations are set to the pump-field intensities, and an analytical approach is presented in the Doppler limit and efficient transverse-optical-pumping regime. It is shown that coherent population trapping due to strong pump-field coupling has a negligible incidence in phase conjugation, while interference of two imbalanced coherent-population-injection channels determines the mixing process. Level-crossing emission resonances are found to exhibit particular line-shape characteristics: (1) an insensitivity to power shifts, (2) strong power-broadening accompanied by incomplete line splitting, or (3) field-induced line-broadening inhibition. The conditions under which these effects should be observable are identified, and their dependence on pump imbalance is remarked.

Applying a perturbation method, constructed in terms of SU(2) group representations, we study spontaneous emission of a system of N identical two-level atoms immersed in a single-mode ideal cavity with s atoms initially inverted. For the cases s≥3, characterized by nonequidistant spectra of the eigenvalues of the Hamiltonian, the phenomenon of collective collapses and revivals manifests itself. For s=3 the approximate solution is compared with the exact one and the limit of good applicability of our method is established.

Recently, a technique [M. Edwards, Phys. Rev. A 45, 409 (1992)] was presented for calculating multiphoton-ionization Green’s functions based on the Wentzel-Kramers-Brillouin (WKB) approximation. In that paper it was shown that the ability of this method to produce accurate cross sections and angular distributions depended critically on the single-particle potential for the valence electron that was used in the calculation. In this work we present a supporting technique for determining the optimal potential for use with this method in low-Z alkali-metal atoms. The technique produces the parameter values for a parametric model potential whose WKB Green’s function has poles that coincide with the measured energy levels of the atom. We have determined the parameter values for a specific model potential in Li and Na. For these cases, only two parameters are needed to produce a potential whose WKB energy levels match all of the measured ones to within 165 ${\mathrm{cm}}^{\mathrm{-}1}$. We have calculated cross sections for two-photon ionization of Li and Na for a range of laser-photon energies using this model potential and present comparisons with previous work.

An effective Hamiltonian for the two-photon two-level model is derived form the microscopic Hamiltonian of a three-level atom in a Λ configuration, interacting through two-photon transitions with a light field. The effective Hamiltonian includes a term describing the optical Stark shift. With this effective Hamiltonian, we study the steady-state equation and the squeezing spectrum for a cavity-field mode interacting with an ensemble of three-level ‘‘Λ-configuration’’ atoms by a two-photon transition. It is shown that significant changes in the transmission characteristics and the squeezing spectrum for the output field result from the inclusion of the Stark shift.

We study the mechanical, dielectric, and nonlinear-optical response of translational optomechanical media to incident electromagnetic radiation. These media consist of three-dimensional arrays of electrically small, isotropic particles that are mechanically supported but free to roll on stacks of very thin transparent planes. Electrostrictive forces tend to move the spheres in such a way as to form spatial variations in the particle density that correspond to electromagnetically induced spatial modulations in the array’s dielectric constant. These modulations constitute translational optical index gratings that can be used to control the propagation characteristics of electromagnetic radiation. We study optical phase conjugation, pump-beam modulation, and harmonic phase conjugation at submillimeter, millimeter, and microwave wavelengths in this class of nonlinear media. We also examine the dynamics of these media from the perspective of the Langevin equations and determine the influence of thermal fluctuations on the properties of such an array.

A homogeneously broadened two-level ring laser with an intracavity parametric amplifier is studied. The presence of the parametric amplifier is shown to lead to two distinct nontrivial cw solutions compared to the one in its absence. The conditions for the stability of these cw solutions are obtained. It is shown that in the context of the resonant modes one cw solution is always phase stable, whereas the other is always phase unstable. For pump parameters beyond a critical value (the second threshold), both these cw solutions become amplitude unstable, and self-pulsing can set in. The shape and the velocity of these pulses are evaluated numerically. It is shown that two distinct types of steady-state pulses beyond the second laser threshold are possible due to the phase sensitivity introduced by the parametric amplifier. This is in sharp contrast to the case without the parametric amplifier, where only Risken-Nummedal pulses [see H. Risken and K. Nummedal, J. Appl. Phys. 39, 4662 (1968)] are possible. It is shown that the parametric amplifier can lead to the narrowing or broadening of the Risken-Nummedal pulses. Moreover, it is shown that the ring laser with or without the parametric amplifier allows for a pulsed solution distinct from the above-mentioned one, which, however, turns out to be unstable.

Conservation laws for Maxwell-Bloch equations applied to describe superfluorescence are studied. Modifications due to the initial boundary conditions are discussed. For initial polarization in the form of a constant tipping angle, conservation laws are integrated to give exact dependence of all field moments on the propagation length. Three regions of propagation are distinguished: the linear region, where the field energy is negligibly small, the region of rapid exponential growth, and the saturation region. The characteristic distance, where maximum radiation occurs, is explicitly evaluated; it defines the threshold length for superfluoresence. A small chirping, proportional to the square of the tipping angle, is found. The change of the pulse width with propagation length is estimated.

The proportionality between the probability for producing a doubly charged ion by photon impact on a neutral atom and electron impact on a singly charged ion is discussed. An energy-dependent parameter is introduced that expands the proportionality from threshold to 500 eV for He and to 360 eV for Ne.

Transitions induced in a quantum system by a periodic interaction are considered from the point of view of scattering theory. It is shown that, if the fully interacting system can be represented by quasiperiodic (Floquet) states, all real (energy-conserving) transition amplitudes must vanish exactly. As an example, the states of a harmonic oscillator in a nonresonant dipole electromagnetic field are shown to have such a representation so that no transitions are possible in this case, which is also the result of a direct calculation of the S matrix.

Absorbers and other beam attenuators inside a neutron interferometer have different influences on the interference pattern, ranging from a stochastic to a deterministic situation. We show that in the quantum limit a smooth transition between both cases is possible. The quantum limit can be approached when using thin absorption gratings, very fast choppers, or rapidly changing fields. The nonremoval probability of neutrons from the original phase space is identified as a crucial quantity describing these phenomena. Experimental results obtained with thin absorption gratings are in agreement with these formulations.

We apply perturbation theory to the Schrödinger equation for a system caged in a one-dimensional box with impenetrable walls and show how to obtain the perturbation corrections to both the energy eigenvalues and eigenfunctions in a systematic exact way when the potential function within the box is a polynomial. As an illustrative example we consider a linear potential obtaining analytic expressions for the perturbation corrections in terms of the quantum number.

Geodesic equations determined by the metric in a projective Hilbert space openP are found. It is shown that connections in the tangent bundle over openP consistent with these geodesics can be introduced. A connection with zero torsion is proposed. Quantum-system dynamics follows the geodesics of another connection which is found for the case of the constant Hamiltonian. A set of geometrical quantities is defined, conserved by a quantum evolution.

Two discrete energy spectra of a particle moving in two different potential wells are compared. We find a general property: If one potential well ${\mathit{V}}_1$(r) is less than or equal to the other potential well ${\mathit{V}}_2$(r) everywhere in space, i.e., ${\mathit{V}}_1$(r)≤${\mathit{V}}_2$(r) for all r, then the nth eigenvalue of the particle in the first well, ${\mathit{V}}_1$, is always not greater than the nth eigenvalue of the particle in the second well, ${\mathit{V}}_2$.

In this paper the order-α contribution of the inner-vertex graph to the decay rate of orthopositronium in the Fried-Yennie gauge is obtained in analytic form.