The interaction of the sodium three-level system with a frequency-fixed or frequency-swept strong laser pulse is studied numerically. The validity of the secular-adiabatic approximation is analyzed. The failure of this approximation, caused by the LS decoupling, for the pulses with the peak Rabi frequency greater than the fine-structure splitting is shown.

We have calculated, by numerically integrating the time-dependent Schrödinger equation, the probability for ionization of a hydrogen atom from a high Rydberg state by a half-cycle pulse whose duration is comparable to, or shorter than, the period of the Rydberg orbit. We have chosen a pulse whose parameters are the same as the pulse used in the experiment of R. R. Jones, D. You, and P. H. Bucksbaum [Phys. Rev. Lett. 70, 1236 (1993)]. We compare our results with the classical results and with the experimental data of Jones et al., and we also present results for energy and angular distributions. Finally, we derive an approximate conservation law which applies in the limit of very short pulse times.

A generalized strong-field approximation is formulated to describe atoms interacting with intense laser fields. We apply it to determine angular distributions of electrons in above-threshold ionization (ATI). The theory treats the effects of an electron rescattering from its parent ion core in a systematic perturbation series. Probability amplitudes for ionization are interpreted in terms of quasiclassical electron trajectories. We demonstrate that contributions from the direct tunneling processes in the absence of rescattering are not sufficient to describe the observed ATI spectra. We show that the high-energy portion of the spectrum, including recently discovered rings (i.e., complex features in the angular distributions of outgoing electrons) are due to rescattering processes. We compare our quasiclassical results with exact numerical solutions.

Ionization of hydrogen Rydberg atoms by circularly polarized microwaves is studied numerically within the framework of classical mechanics. Both the simplified two-dimensional model (in which the plane of polarization coincides with the orbit plane) and a fully three-dimensional system are considered. It is shown that the ionization proceeds in the diffusive manner for all microwave frequencies except the low-frequency limit. The threshold for diffusive excitation as well as the diffusion speed is strongly dependent on the initial state of the system for smooth pulse excitation. In a high-frequency limit the ionization threshold rises sharply—the atom is much more resistant to the excitation. Two distinct regimes of stabilization windows (regions where the ionization decreases with increasing field amplitude), one in the strong short-laser-pulse domain and the other in the weak microwave domain, are identified and discussed.

We consider propagation of a light beam in photorefractive media in the framework of a three-dimensional model. We formulate equations governing three-dimensional distribution of a nonlinear refractive index. The distributions of electric charge, potential, current, refractive index, and the near- and far-field output intensities of the beam are calculated. The conditions necessary for observing self-focusing in photorefractive media are discussed.

We report the results of experimental and theoretical studies of the laser-induced birefrigence of concentrated suspensions of shaped, anisotropic artificial Kerr media. The systems we investigate experimentally are aqueous suspensions of polytetrafluoroethylene (PTFE). The observed slowing down of the relaxation of the birefringence signal is in agreement with pretransitional behavior near the isotropic-nematic phase transition. However, in order to explain the relatively small increase of the induced birefringence with an increase in concentration, and the double exponential character of relaxation, one should include the possible deviation of the optical axis from the geometrical, or long, axis of the PTFE particles.

We examine the spatiotemporal dynamics of the optical field that arises from two-wave mixing in a multiple-transverse-mode unidirectional photorefractive ring resonator. Using the passive resonator’s transverse modes as a basis, we derive a set of differential equations that describes the mode dynamics when both pump-mode and mode-mode gratings are formed. In the absence of intermodal gratings, this set reduces to the Hopf bifurcation equations for nonlinear mode interactions. We have performed two and three transverse-mode experiments using a photorefractive ring resonator with an Fe:${\mathrm{KNbO}}_3$ crystal. Numerically simulated coupled-mode dynamics are shown to have good correspondence with the experimental data.

We show numerically that, contrary to what has been believed so far, multidimensional quasisolitons can propagate in cubic nonlinear media. To avoid the blowup along the propagation axis, we take advantage of cross-phase modulations and two-wave parametric interactions under a balanced photon exchange. A compact analytical expression for the new solitons with arbitrary transverse dimension is derived through self-consistent-field approximation.

van der Waals interactions between atoms and dielectric surfaces are reinvestigated. To describe the nonretarded interaction potential between a dispersive dielectric surface and an atom in an arbitrary internal energy state, we derive a general expression in terms of an integral, over real frequency, of the combined atom and surface polarizabilities. It is shown that, for excited atoms, the expression is equivalent to the one obtained by Wylie and Sipe [Phys. Rev. A 32, 2030 (1985)]. We thus demonstrate how to extend this approach to excited atoms interacting with birefringent dielectrics. For isotropic dielectrics, a method of integration in closed form allows us to derive an approximate formula for the van der Waals interaction constant in terms of resonance frequencies and oscillator strengths of both the atom and the dielectric. Frequency-dependent ‘‘dielectric reflection’’ coefficients are introduced for virtual atomic dipole couplings either in absorption or in emission. In absorption, the reflection coefficient is always positive and smaller than unity. In emission, it may take arbitrary values, positive or negative (corresponding to van der Waals repulsion). Such a behavior is shown to be related to resonant excitation exchange between the atomic system and the dielectric medium, when an atomic transition frequency gets in resonance with a dielectric absorption band. Numerical calculations performed for the cesium-sapphire system are shown to be in good agreement with data obtained by selective-reflection spectroscopy. Finally, experimental tests of the birefringent character of the sapphire response are discussed.

Taking into account the nonlinear loss and nonlinear refraction-index change due to medium ionization, high-power pulse amplification is studied under coherent conditions. An exact self-phase-modulated steady-state pulse solution is found for the coupled Maxwell-Bloch equations with a nonlinear loss and refraction-index change caused by the medium ionization, representing a generalization of the known π-pulse solution. The ultimate parameters of an amplifier as maximum pulse energy or minimum pulse duration are estimated and compared with experimental data.

A nonlinear optical phenomenon, namely, the surface waves in photorefractive crystals with a diffusion nonlinearity (of the gradient type), is suggested and analyzed. These waves can be guided along the boundary of the crystal with a metal, a dielectric with a lower average refractive index, or a similar photorefractive crystal with the opposite sign of the diffusion nonlinearity. Our estimates predict that for a typical photorefractive crystal such as ${\mathrm{BaTiO}}_3$ this mechanism can ensure efficient concentration of light power in a crystal layer of ∼10 μm thickness.

A scheme for the preparation of Fock states and general superposition states of the electromagnetic field in a cavity is studied in detail. The scheme uses adiabatic passage in a strongly coupled atom-cavity system to ‘‘map’’ atomic ground-state Zeeman coherence onto the cavity-mode field. We model photon-counting and homodyne measurements of the field exiting the cavity and demonstrate the possibility of generating and detecting highly nonclassical states of the field parameter values close to currently realizable experimental values. The adiabatic passage process is also reversible, enabling cavity-mode fields to be mapped onto atomic ground-state Zeeman coherence. Application of this property to the measurement of cavity fields is discussed, with particular consideration given to a possible scheme for quantum measurements of the intracavity photon number.

Atkins and Dobson [Proc. R. Soc. London Ser. A 321, 321 (1971)] have constructed coherent angular-momentum states using the Schwinger bosonic representation and operating the displacement (coherent) operator on both of the bosonic vacuum states. By performing a squeezing transformation on the bosonic coherent states we generalize the idea of Schwinger angular-momentum coherent (SAMC) states to Schwinger angular-momentum squeezed (SAMS) states. We show that these SAMS states, which are constructed from the bosonic squeezed coherent states, exhibit squeezing of Schwinger angular-momentum operators under a certain range of parameters. The properties of these states are studied and compared with their single-mode bosonic counterpart. Application of these states in increasing the accuracy of an interferometer is discussed.

The investigation of photon statistics and quadrature squeezing in superpositions of two coherent states under the influence of a continuous measurement of photon number shows that the photon statistics of the cavity mode oscillates between sub-Poissonian and super-Poissonian distributions and that the quadrature fluctuation oscillates between squeezing and nonsqueezing at each time when one photon of a cavity mode is registered by a counter. These oscillatory behaviors are caused by the influence of the continuous measurement of photon number and the quantum interference between the two coherent states in the superposition.

The time evolution, under the general time-dependent quadratic quantum Hamiltonian, of mean values of a class of observables that includes the field quadratures and their dispersions, is obtained exactly in classical Hamiltonian form. Quantum states are described in terms of density operators, so that arbitrary initial states (both pure states and statistical mixtures) are allowed.

When two electron conduction subbands in a doped quantum well are coupled by a coherent laser pumping, electromagnetically induced transparency and Rabi splitting in the interband absorption spectrum of a probe light are found for steady electron dressed states. The effect of light-electron interaction on electron and hole eigenenergies and states are calculated using a generalized density-functional approach. The change of absorption coefficient with the pump field amplitude is studied and explained.

A measure for the distance between two arbitrary density operators, based on the Hilbert-Schmidt norm, is investigated. It is applied to the Jaynes-Cummings model where the question of the extent to which a given state is close to the initial state or to another state of interest has commanded a lot of attention. This problem is studied in detail for the whole system as well as for the field and the atom subsystems. The behavior of the distance for some important particular cases is numerically evaluated. Some interesting aspects of the field and the atom dynamics are discovered.

The stimulated parametric-down-conversion luminescence is used as a light source with controlled spatial coherence. Performing the double-slit Young experiment, we show that the interference-pattern visibilities can be controlled by varying the inducing laser intensity. The results indicate that down-conversion light statistics change during this variation. A simple theoretical description is also shown.

The quantum theory of light propagation in a Kerr medium is applied to describe changes in the polarization state of light. A number of purely quantum effects arising during the propagation are analyzed. Stokes operators and Pegg-Barnett formalism are used to describe the evolution of the polarization ellipse. The predictions of these approaches are compared, showing some striking differences in the quantum regime of small photon numbers.

We derive the master equations for the fields in the one-mode Λ-type micromaser and laser with injected atoms in a superposition of their states. In terms of effective parameters, these equations are equivalent to those for a two-level micromaser and laser. The interference terms in the master equations may cancel the absorption terms independent of statistical properties of the field. Due to the atomic coherence between the two degenerate lower levels, the generation of field states with sub-Poissonian photon statistics is possible in the micromaser without the need for a population inversion. If an equivalent level system is used in a laser operating without population inversion it can produce field states with Poisson distributions of the photon number.