We have investigated the mean-field approach to the vibron model. The link between the algebraic description of molecular vibrations, as described by the vibron model, and the usual variables in configuration space has been used to extract the dipole-moment function of diatomic molecules. A comparison is shown between the vibron-model results and the experimentally derived dipole-moment function for HF.

The electron-positron pairs observed in heavy-ion collisions at Gesellschaft für Schwerionen-forschung Darmstadt mbH have been interpreted as the decay products of yet unknown particles with masses around 1.8 MeV. The negative results of resonant Bhabha scattering experiments, however, do not support such an interpretation. Therefore we focus on a more complex decay scenario, where the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ lines result from a two-collision process. We discuss the induced decay of a metastable $1^{++}$ state into ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ pairs. For most realizations of a $1^{++}$ state such a decay in leading order can only take place in the Coulomb field of a target atom. This fact has the attractive consequence that for such a state the Bhabha bounds are no longer valid. However, the absolute value of the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ production cross section turns out to be unacceptably small.

Coherently pumped far-infrared ring lasers with pump and laser fields having crossed linear polarizations are known to exhibit type-I intermittent dynamics [D. Y. Tang, M. Y. Li, and C. O. Weiss, Phys. Rev. A 46, 676 (1992)]. We study here a homogeneously broadened four-level model for these laser systems. For a small range of parameters our model also shows a type-I intermittency route to chaos, but a complete agreement with their experimental results is not achieved.

The Thomas-Reiche-Kuhn sum rule is corrected for the motion of the atomic center of mass, and generalized to include ions. The results are specialized to the case of a two-level atom or ion.

We show that such phenomena of laser dynamics as mean-phase-slope jumps and temporal phase jumps at resonance between the cavity and spectral line frequencies are intrinsically connected with the topology of attractors in the space of rays and can be interpreted as the manifestations of the geometric-phase properties of the evolution operator.

Using a simple version of the model for the quantum measurement of a two-level system, the contention of Aharonov, Anandan, and Vaidman [Phys. Rev. A 47, 4616 (1993)] that one must in certain circumstances give the wave function an ontological as well as an epistemological significance is examined. I decide that their argument that the wave function of a system can be measured on a single system fails to establish the key point and that what they demonstrate is the ontological significance of certain operators in the theory, with the wave function playing its usual epistemological role.

It is pointed out that deformation parameters in a generalized deformed boson algebra should satisfy some restricted conditions; otherwise negative norm states will appear in the model space.

Usual quantum-optical operator relations for a beam splitter are shown to lead to an anomalous commutation relation inside a microcavity. The physical origin of this anomaly is identified as self-interference of the mode whose coherence length is longer than the round-trip length of the cavity. Altered spontaneous emission of an excited atom is found to be a direct manifestation of this anomalous commutation relation. The anomalous Heisenberg uncertainty relations, which are derived from the commutation relation according to the Schwartz inequality, cannot be detected by probing the internal field with a beam splitter. The anomalous commutation relation, however, can be related to the change in the effecitve reflectivity of the beam splitter. The similarity and difference between an excited atom and a probe beam splitter are discussed.

We point out that the condition imposed on the deformation parameters by the preceding Comment [Pan, Phys. Rev. A 50, 888 (1994)] does not affect the validity of the fits of the commented work [Bonatsos and Daskaloyannis, Phys. Rev. A 46, 75 (1992)]. Furthermore, we point out a way of avoiding both the condition on the parameters and the appearance of negative norm states simultaneously.

We analyze the quantum density of states for a system of coupled quartic oscillators in the vicinity of symmetric isochronous or pitchfork bifurcations of the primary oscillator modes. A uniform semiclassical expression for the contribution to the density of states from the set of periodic orbits involved in the bifurcation is derived following the approach of Ozorio de Almeida and Hannay [J. Phys. A 20, 5873 (1987)] and Ozorio de Almeida and Aguiar [Physica D 41, 391 (1990)].

A simple gedanken experiment, the motion of a bead inside a rotating linear pipe, is considered. It is shown that at large enough velocities a centrifugal force acting on the bead changes its usual sign and attracts towards the rotation axis. The motion of the bead is oscillatory, resembling a well-known case of the mathematical pendulum. A possible relevance of this highly idealized problem to the real motion of charged particles in a pulsar magnetosphere is pointed out.

Triple differential cross sections are presented for the electron-impact ionization of silver and gold in coplanar asymmetric geometry at an impact energy of 500 keV. The problem is treated in a completely relativistic manner, using Dirac distorted waves in both the incident and final channels and the full photon propagator. Good agreement with experiment is obtained.

We present experimental evidence that the spontaneous transverse filamentation of a laser beam back reflected onto a thin Kerr optical medium can be strongly affected by the actual boundary conditions, namely the Gaussian shape of the beam. As the filament spacing is made to increase by moving the feedback mirror, well-known hexagonal patterns no longer grow up but rather the laser spot breaks up into lower dihedral symmetry patterns, such as pentagonal, rhombic, or triangular ones, in very good agreement with previous numerical predictions. Further increasing the laser intensity after the symmetry breaking leads to secondary bifurcations. The multistability, itineracy, and turbulence of those structures were also observed.

The use of a free-electron laser (FEL) allows the study of (non)linear optical properties of materials over unsurpassed large spectral intervals. Here we report on the application of a FEL as the IR source in spectroscopic infrared-visible sum-frequency generation (SFG). Using the extremely wide tunability and the high peak power of a FEL we have studied the frequency dependence of the nonlinear susceptibility for sum-frequency generation in gallium phosphide between 20 and 32 μm in great detail. It is shown that the SFG spectrum is heavily modified by linear optical effects.

Using supersymmetry quantum mechanics, we explain the covariance of the eigenvalue equation for the Jaynes-Cummings (JC) Hamiltonian under the particle-hole transformation. The JC Hamiltonians for the original spin-1/2 ‘‘particle’’ and the transformed partner (the ‘‘hole’’) are shown to be the fermionic and the bosonic parts of a supersymmetric Hamiltonian. The Hamiltonian, unlike ordinary one-dimensional supersymmetric quantum-mechanical models, can have a degenerate zero-energy ground state despite exact supersymmetry. The degeneracy is shown to arise from the hidden particle-hole exchange symmetry as well as supersymmetry in the Hamiltonian.

Differences in the dissociative ionization pattern of ${\mathrm{CH}}_4$ obtained in interactions with intense laser fields, and by fast-ion impact, are discussed in terms of molecular-alignment effects.

The vortex structure of the steady-state probability flow for a general one-particle system in quantum mechanics is introduced and its relationship to the inverse-square potential is discussed. The relationship is made clear by classifying the corresponding solutions of the related classical inverse-square-potential problem.

A systematic procedure to define and/or classify local transmission and reflection times for the passage of a quantum particle through a static potential barrier is described. Previously defined times and new quantities arise as particular cases of the general formalism. Generalizations for multidimensional and multichannel scattering systems are presented. The one-dimensional results are applied in detail to the rectangular potential. Other nonlocal approaches based on the current density are also examined, and the ‘‘Hartman effect’’ is quantitatively characterized for wave packets.