Amplitude-squared squeezing has been investigated for the generalized multiphoton Jaynes-Cummings model. Different values for the initial photon numbers as well as different photon multiplicities have been used. The atom is taken to be in either the ground or the excited state. The relation between both amplitude-squared and normal squeezing and the phenomenon of collapse and revival has been discussed.

A quantum theory of nondegenerate four-wave mixing is developed and applied to study a highly excited semiconductor resonator operating below or near the laser threshold. It is found that total carrier-density pulsations allow coherent effects in semiconductors despite the rapid decay of the electron-hole correlations. The output spectrum for a nondegenerate four-wave mixing intracavity experiment is computed and squeezing in the sidemode spectrum is predicted.

It is shown that strong competition between the absorption and emission of the cavity photons and the incoherent processes like atomic spontaneous emission and cavity decay effects result in new nonequilibrium states in cavity quantum electrodynamics. Such states can exhibit saturation, nonclassical character, and strong atom-cavity correlation.

The fluctuations in the phase of the pump in a degenerate optical parametric oscillator are modeled by a classical phase-diffusion process, and their influence on squeezing is studied. To this end, appropriate quadrature variables, relative to the instantaneous phase of the pump, are introduced. The squeezing is calculated both inside and outside the cavity. In both cases it is found to be degraded by the phase fluctuations, which may be understood in terms of the time lag in the response of the system to an instantaneous change in the pump phase. This effect might account for a small part of the residual noise present in current experiments. Correlation functions for the field of the oscillator for finite pump linewidth are derived and discussed.

The question of nonlinear transient effects similar to self-induced transparency and adiabatic following is examined for a moving Rydberg atom undergoing two-photon transition in a lossless cavity having spatial field distribution. Also, comparison is made with the case where an atom is undergoing one-photon transitions under similar conditions.

It is demonstrated that the dynamics of small-amplitude dark solitons in the presence of the stimulated Raman effect in optical fibers may be described by the well-known Korteweg–de Vries–Burgers equation. This approach allows us to explain analytically the temporal self-shift of dark solutions due to self-induced Raman scattering and to predict oscillating shock waves in optical fibers.

We consider cooperative spontaneous emission by an assembly of N two-level atoms immersed in a high-Q single-mode cavity, when s (s≪N) atoms are initially excited. The atoms are noninteracting with each other except via the action of the electromagnetic field. The eigenvalues of the system and the time development of the mean energy of the atomic subsystem are presented in the form of power series in the parameter ε=(N-s/2+1/2${)}^{\mathrm{-}1}$ using the SU(2)-group-representation technique.

An earlier equivalent-particle theory, describing the propagation of a self-focused light channel at an oblique angle of incidence to the interface separating two nonlinear dielectric media [A. B. Aceves, J. V. Moloney, and A. C. Newell, J. Opt. Soc. Am. B 5, 559 (1988); Phys. Lett. A 129, 231 (1988); Phys. Rev. A 39, 1809 (1989); 39, 1828 (1989)], is extended to include diffusion of the nonlinear excitation within each medium. The theory replaces the computationally intensive problem of beam propagation by the much simpler and intuitive picture of the motion of an equivalent particle in an equivalent potential. This simpler Newtonian dynamical problem provides quantitative information on the asymptotes of the reflected, transmitted, or trapped channels as well as the stability of the latter as a function of increasing diffusion length. Our main results are that increased diffusion makes light transmission more difficult and tends to wash out the local equilibria of the equivalent potential representing unstable or stable TE nonlinear surface waves.

Molecular polarizability theory with the inclusion of the second-hyperpolarizability coefficient is used to study the transient generation of four-wave- and six-wave-mixing signals when a system interacts with laser and Stokes pulses of frequencies ${\mathrm{\omega }}_{\mathit{l}}$ and ${\mathrm{\omega }}_{\mathit{S}}$ lying in the region of the subharmonic Raman resonance ${\mathrm{\omega }}_{\mathit{l}}$-${\mathrm{\omega }}_{\mathit{S}}$≊${\mathrm{\omega }}_{\mathit{R}}$/2. The dynamical equations for various fields and amplitudes of the Raman and the subharmonic mode are derived and integrated numerically to obtain the detailed characteristics, such as pulse width, pulse center, ringing, etc., of the generated signals. The effect of the chirp in the incident pump pulse is also studied.

Cross sections for antihydrogen formation for the process p¯+Ps→H¯+e have been calculated utilizing the charge-conjugation and time-reversal invariance as suggested by Humberston et al. [J. Phys. B 20, L25 (1987)]. Calculations are performed in the framework of the eikonal approximation for a wide range of antiproton energy (20–11 000 keV).

Because of the growing need of excitation cross-section data of atomic hydrogen by fully stripped heavy ions for the preparation of an atomic database for neutral-beam penetration in large tokamaks, we have calculated these data in the framework of the first-order Born approximation for n≤20 in the energy range of 0.1 to 1.5 MeV/amu. The present computed results are found to be in agreement with the existing observed results. From the present calculation it also appears that the contribution from subshells characterized by l>3 is always less than 2%.

3p Coster-Kronig decay of Rb(Z=37) has been studied by comparing the new experimental and theoretical decay widths with earlier predictions and with the results for the neighboring atom Kr(Z=36). The insensitivity of the Coster-Kronig single-channel transition rate around Z=37 to the choice of orbitals and transition energy has been discussed. The reliability of the intermediate-coupling calculations in determining the experimental Coster-Kronig level widths has been called into question.

Calculations employing the independent-electron approximation suggest that direct Coulomb ionization is the dominant mechanism for Ar K-vacancy production by 47-MeV ${\mathrm{Ca}}^{17+}$, rather than K-K vacancy sharing as proposed by Schlachter et al. [J. Phys. B 21, L291 (1988)]. Using electron-capture probabilities for zero impact parameter given by the classical-trajectory Monte Carlo model, good agreement with the experimental charge-state distribution for multielectron capture in coincidence with Ar and Ca K x rays is achieved.

Cross sections for the nondissociative single ionization and double ionization of ${\mathrm{H}}_2$ by ${\mathrm{He}}^{2+}$ projectiles in the range of 125–750 keV/amu are reported. The results are compared to impact-parameter calculations and to measurements with ${\mathrm{He}}^{+}$ projectiles. The direct double-collision process is found to be the important contributor to double ionization in this range of energies. The single-ionization cross section, when compared to proton bombardment, does not scale as ${\mathit{Z}}^2$.

We have extended our earlier investigation on asymmetric collisions in the framework of a modified peaking impulse approximation for the case of collisions of fully stripped ions of helium and lithium with carbon and neon. As the charge of the projectile is high, we propose to find an exact estimate of the contribution of charge transfer into higher excited states of the projectile. The contribution of charge transfer into n=2 states is never found to exceed 12% in the entire energy region of 0.3–3.0 MeV/amu. Total cross sections compare fairly well with existing experimental results.

The screening of a slow antiproton in an electron gas is discussed as an analogy of dielectric response formulation. A simple parametric form of the dielectric function is proposed that leads to analytic expressions for the effective potential and induced hole density. The parameter is fixed via the cusp condition for the total electron density at the position of the probe charge. The stopping power is calculated by making use of the transport cross section. The results are in fair agreement with those given by a recent self-consistent calculation.

A series of nonsingular Coulomb potentials is found that admits exact analytic solutions. The form of the potentials is V’=-${\mathit{Ze}}^2$/(r+a) with specific choices for the cutoff parameter a, which does not have the troublesome singularity at r=0 but retains the long-range feature of the Coulomb interaction. Determination of the parameter a and construction of the analytic solutions are discussed in detail. Applications to laser-induced dressing of atomic states are considered.

The effects of quantum noise on a two-level system in the bad-cavity regime are considered perturbatively in the form of closure at the pair-correlation level. It is found that pair-correlation effects can reduce the level of semiclassical chaos. However, under the rotating-wave approximation (RWA), quantum noise can lead to chaos if there is an initial population inversion, while the full RWA Hamiltonian system remains integrable.

The joint probability of detecting simultaneously three photons at three different points in the superposition field of two independent plane waves with random phases is calculated and compared with the results of a classical wave theory. There are important differences when the number of photons is small. In particular, if there is one photon in one beam and two photons in the other one, three photodetectors can be placed at positions such that all three never respond at once, even though one beam intensity is two times stronger than the other.

The isoelectronic exposition of atomic structure properties involves labeling ambiguities when more than one level of the same total angular momentum and parity is present, and an energy ordered labeling of these levels can lead to apparent isoelectronic discontinuities. For example, in the recent oscillator strength calculations for S-like ions by Saloman and Kim [Phys. Rev. A 38, 577 (1988)], abrupt changes in the rates were sometimes observed between one isoelectronic element and the next. We suggest an alternative labeling scheme that removes these discontinuities and produces a smooth isoelectronic variation. This alternative labeling offers advantages for data exposition and for semiempirical interpolation and extrapolation.