A complex-scaling Fourier-grid Hamiltonian (CSFGH) method in momentum representation along with Floquet formalism is presented and applied to the nonperturbative treatment of the complex quasienergies of a one-dimensional-model negative chlorine ion in an ArF excimer-laser field. The CSFGH method leads to a simple and highly efficient variational procedure for accurate determination of resonance states, without the need of using an ${\mathit{L}}^2$-basis-function expansion. A variety of laser intensities are considered covering those from perturbative to very intense laser fields, and the stability of the ion is investigated under realistic experimental conditions. Oscillatory structures of the photodetachment rate as a function of field strength are found in our study, revealing that the decreasing of the detachment rate (or the so-called ‘‘stabilization’’ or ‘‘suppression-of-ionization’’ phenomenon) may not necessarily be a monotonic behavior. Physical insight into this interesting feature is explored in the Kramers-Henneberger frame, and the feasibility for the experimental observation of the oscillatory behavior of the negative ions is also discussed.

Isotopic studies of multiphoton ionization of ${\mathrm{N}}_2$O give clear evidence for a significant atomic site selectivity in the production of atomic fragments. The observation of the diatomic fragments ${\mathrm{N}}_2^{+}$ and ${\mathrm{NO}}^{+}$ suggests a possible role for curve-crossing mechanisms that could lead to electronically excited fragments.

We show, through a simple model, that as one changes the detuning of a standing-wave single-mode gas laser containing an inhomogeneously broadened saturable absorber, a Lamb-dip generated stability window may appear in the instability region. The width of this window is of the order of the homogeneous linewidth of the absorber, and it is not affected by power broadening.

We observe significant lifetime modification (both reduction and lengthening) of 610–620-nm light spontaneously emitted by chelated europium ions in 10-μm-diam dimethylformamide-alcohol solution droplets. The enhancement or inhibition of the Einstein A coefficient over the familiar free-space value is direct evidence of cavity quantum-electrodynamic effects taking place in microdroplets.

A tabletop x-ray laser scheme involving lasing to the ground state of an ion following optical-field-induced ionization by a high-intensity short-pulse laser is studied. The role of the ground state in reducing the saturation intensity is calculated to be larger for H-like ions as compared with the effect in Li-like ions. Energy efficiencies of order ${10}^{\mathrm{-}5}$ are calculated for the 3${\mathit{d}}_{5/2\mathrm{-}}$2${\mathit{p}}_{3/2}$ transition at 98 Å in Li-like Ne. The efficiency calculations are based on a driving laser with an intensity of 3×${10}^{17}$ W/${\mathrm{cm}}^2$, a wavelength of 0.25 μm, a pulse duration of 100 fsec, and an input energy of 25–100 mJ. A correction to the standard stimulated Raman scattering growth rate is given for a finite laser pulse. Use of short pulses is shown to be sufficient to control heating from stimulated Raman scattering in Li-like Ne. Extending the scheme to shorter wavelengths (e.g., Li-like Al at 52 Å) is difficult because of reduced efficiencies and excessive electron heating from Raman scattering.

Experimental realizations of standard models in the field of ‘‘quantum chaos’’ are proposed. These are dielectric waveguides that are periodically perturbed along the direction of propagation. The direction of propagation corresponds to time in the quantum chaos problems. The periodic perturbation leads to transitions between the modes of the unperturbed problem as is the case for the quantum chaos problems. The system exhibits chaotic behavior in the limit of geometrical optics, corresponding to classical mechanics. In the quantum chaos problems wave effects suppress this chaotic behavior and lead to localization in mode space. It is found that for a wide range of experimental parameters the behavior of the system is determined by two parameters, corresponding to the stochasticity parameter and Planck’s constant in the quantum chaos problems. The correspondence between these problems is investigated in detail and the limits of its validity are studied. Detailed analytical and numerical calculations are presented in a regime of parameters that may be of experimental interest, for planar waveguides and for circular fibers.

We study the first-order perturbation contribution of a generic Markovian master equation on a general superposed quantum state. From this we obtain a universal formula describing the decay of quantum superpositions for arbitrary quantum superpositions. For single-photon damping, superposed coherent states appear, naively, to give the smallest damping rate. However, a comparison of damping rates, based on the observability of superposition fringes, shows that superposed squeezed states can do significantly better than their coherent state rivals. The optimum squeezed superposition is shown to have a damping rate (for the zero-temperature Markovian master equation) linear in the phase-space distance between the pieces of the original unsqueezed superposition, as compared with the quadratic dependence for superpositions of coherent states. Finally, we show that superpositions of squeezed states can be generated directly from squeezed states without having to squeeze a superposition.

The nonlinear Mach-Zehnder interferometer is presented as a device whereby a pair of coherent states can be transformed into an entangled superposition of coherent states for which the notion of entanglement is generalized to include nonorthogonal, but distinct, component states. Each mode is directed to a homodyne detector. We show that there exist nonclassical intensity correlations at the output ports of the homodyne detectors which facilitate a test of local realism. In contradistinction to previous optical schemes which test local realism, the initial state used here possesses a positive Glauber-Sudarshan representation and is therefore a semiclassical state. The nonlinearity itself is responsible for generating the nonclassical state.

A simple nonlinear generalization of the Jaynes-Cummings model is investigated within the rotating-wave approximation. The dynamics of the system (the quantum inversion and squeezing of radiation) is discussed. Due to the nonlinearity, for certain values of the detuning the quantum inversion does not exhibit the Cummings collapse. Instead, additional structures in the very-long-time behavior of the system appear.

The interaction of spin-1/2 atoms in an optical resonator with a near-resonant cw light field and an external static magnetic field gives rise to self-sustained spin precession. This entails a modulation on the transmitted light at roughly the Larmor frequency. We show that under suitable conditions this oscillation can become irregular. A detailed analysis reveals a deterministically chaotic process. Dimensions, entropies, and Lyapunov exponents are determined; cross-checks demonstrate their mutual consistency. To describe the observed dynamics, a three-dimensional model is presented that resembles the well-known Bloch equations. Numerical simulations compare well with the experimental results. Of all the nonlinear terms in the model, the one describing the light shift can be singled out as responsible for the chaotic behavior. This allows an intuitive understanding of the onset of chaos as a result of the interaction between spin precession and light shift.

The approximate formulas of the mean, variance, and skewness of first-passage-time distributions for a single-mode dye laser are derived. The explicit expressions of these quantities for the white-loss-noise model (model A) and the white-gain-noise model (model B) are obtained. We find that (1) the mean first-passage time for models A and B are indistinguishable; (2) as the laser intensity is increased, the increase of the variance and skewness of models A and B are faster than those obtained from the cubic model; (3) as the laser intensity is increased, the increase of variance and skewness in the white-gain-noise model are slower than those obtained from the white-loss-noise model. Therefore the effect of the fluctuating saturation term in model B seems to weaken the increase of the variance and skewness.

We have derived the approximate formulas of the mean, variance, and skewness of the first-passage-time distribution for the colored-loss-noise model and the colored-gain-noise model of the dye laser by virtue of the best Fokker-Planck-equation approximation. Comparing the colored-loss-noise model with the colored cubic model, it is shown that our analytic results are in good agreement with the numerical simulation given by Zhu, Yu, and Roy [Phys. Rev. A 34, 4333 (1986)]. We find that the prefactor of the pump fluctuation term can curb the variance and skewness of the first-passage-time distribution. In the regime 0.8<${\mathit{I}}_0$<1, where ${\mathit{I}}_0$ denotes the relative laser intensity, the best Fokker-Planck equation predicts that as the laser intensity is increased, the increases of the variance and skewness of the first-passage-time distribution for the colored saturation models are slower than those of corresponding white saturation models.

We study an atomic system interacting with a broadband squeezed vacuum and several applied classical fields. Exact rate equations are derived from the Gardiner-Collett master equation. A diagrammatic analysis is presented, which enables one to write down the contributions in a relatively simple manner and to provide a physical interpretation of the various terms. The method is applied in the following paper [Smart and Swain, Phys. Rev. A 45, 6863 (1992)] to a study of resonance fluorescence.

We study the system of a single two-level atom interacting with a braodband squeezed vacuum and a classical applied field. The atom is subject to collisions, and the applied field may possess a finite linewidth. The atomic populations, coherences, resonance fluorescence spectrum, and intensity fluctuation spectrum are calculated. Wherever practicable, analytic expressions are obtained that show the dependence of these quantities on the damping parameters. Numerical plots are presented. Two qualitative results that we obtain are the following: (a) we show that the dependence of the populations on the squeezing phase is increased by increasing the damping parameters, contrary to what might at first have been expected, and (b) we show that, in the absence of external damping, the squeezing induces strong asymmetries in the off-resonant resonance fluorescence spectra.

We discuss the possibility of narrowing the atomic autoionization states via their resonance mixing in a field. The results show that, in contrast to the interference process [Yu. I. Geller and A. K. Popov, Laser Stimulation of Nonlinear Resonances in Continuous Spectra (Nauka, Novosibirsk, 1981)] or to the mixing of two isolated states [A. I. Andryushin et al., Sov. Phys.—JETP 61, 678 (1985)], with mixing of multiplets one may expect substantial narrowing of autoionization states owing to their intersection with bound-electron states.

The current density is calculated exactly for independent harmonically confined electrons in a constant magnetic field. The conclusion is that a steady current is induced by a magnetic field on the nonuniform charge distribution characterizing this model.

The Eckhaus equation i${\mathrm{\psi }}_{\mathit{X}}$+${\mathrm{\psi }}_{\mathit{T}\mathit{T}}$=${\mathit{a}}_2$ψ‖ψ${\mathrm{\Vert }}^4$+(${\mathit{a}}_4$+${\mathit{ia}}_5$)ψ (‖ψ${\mathrm{\Vert }}^2$${)}_{\mathit{T}}$ is reduced to an ordinary differential equation that is solved exactly, whenever possible, and approximately using a variational method. The approximate solutions describe a nonlinear generalization of the Weber-Hermite modes of the linear model.

For a system in a well with a moving boundary, we show that the state of the system memorizes the history of the motion of the boundary through a nonintegrable phase factor, the Berry phase.

Positronium formation in the n=1 and n=2 levels in ${\mathit{e}}^{+}$-He collision has been studied using a second-order Born approximation. Differential and integrated capture cross sections are reported in the energy range 100 eV–2 keV. The predicted total positronium-formation cross sections differ from measured values, the theoretical results being lower. The first-order Born results are not expected to be valid in the energy range considered. A Thomas mechanism is found to be valid in the case of the ground as well as the 2s excited state. A similar structure in the differential cross section for 2p-state capture has not been found.

A model correlation factor is used to derive an exchange-correlation functional. The factor satisfies the cusp condition and the normalization of the second-order density matrix. No use is made of the homogeneous-electron-density approximation. Results for several atoms and ions show the feasibility of the approach.