We present a general formalism that incorporates local-field corrections into Bloch’s equations and use it to calculate the strong-field susceptibility of a pressure-broadened gas consisting of two-level atoms. The major effect is to introduce a dynamic Lorentz shift that varies throughout the resonance line shape. We also calculate the susceptibility associated with a weak field (probe) in the presence of a strong field (pump) when the pump and probe are at the same frequency. Here the effect is to introduce both a variable shift and a greater distortion of the line shape.

We report the results of a numerical study of nearly-single-mode semiconductor lasers. The stochastic nonlinear dynamical equations of the field and population inversion are integrated and the intensity fluctuations and line shapes of the laser are investigated. The second mode affects the coherence of the light output appreciably, particularly near the laser threshold regime. The accuracy of the linearized theory for a single-mode laser is tested from far below to far above threshold. It is found to be very accurate both far below and far above threshold, but significant discrepancies are seen in the threshold region. We automatically include the coupling of the intensity and phase fluctuations in the line-shape calculations, resulting in the experimentally observed asymmetry of the relaxation oscillation sidebands. The numerical technique developed here is easily applicable to multimode lasers and is shown to be a convenient and powerful probe of the coherence properties of semiconductor lasers.

A semiclassical treatment of the radiation loss in a laser, previously investigated by Baseia and Nussenzveig [Opt. Acta 31, 39 (1984)], is extended to the quantum-theory level. The model employs an optical cavity having an output coupling that includes the radiation loss due to the beam extraction through appropriate boundary conditions, instead of the unrealistic loss reservoir of the conventional treatment. This allows one to work entirely within the continuous spectrum and obtain the equation for the radiation field both inside and outside the cavity. Inside the cavity the results agree, in the coherent representation and absence of quantum noise, with those of the previous semiclassical theory. Also, the results of both treatments for the field inside the cavity coincide with those of the conventional theory, since we reinterpret its ‘‘mode amplitude’’ as a collective variable. Outside the cavity (an inaccessible region for a standard approach) the explicit solution for the laser field exhibits a natural relationship between the intensities inside and outside the cavity. Further considerations, such as those concerning the role played by the noise term in the field buildup, are also discussed.

We present a semiclassical theory of the micromaser by using a consistent multiple-time-scale expansion of its dynamics. The time scale over which the semiclassical approximation is valid is established, and the effects of quantum and thermal fluctuations in the long-time limit are investigated. A thermodynamical analogy is introduced to interpret the steady-state properties of the micromaser, and we show that a simple model allowing for two-phase coexistence provides the best agreement between the semiclassical and quantum theories.

We use our interpretation of homodyne and heterodyne detection of squeezed states, viz., quantum correlation between photons as expressed in second-order correlation functions, to study various cases. In particular, we introduce the coherence time of the local oscillator and show its influence on the possible noise reduction. We also study the case in which the local oscillator is not much stronger than the squeezed state and analyze the influence of phase jitter. This approach could explain some experimental results and suggest improvements in detection schemes.

Efficiency enhancement in an electron cyclotron autoresonance maser (CARM) amplifier through magnetic field tapering is investigated using computer simulations. Depending on the initial frequency mismatch, tapering the magnetic field with either a negative or positive gradient can enhance the efficiency over that of the resonantly tuned CARM. Tapering, however, has little effect in further increasing the efficiency of the optimally detuned device. Tapering also becomes ineffective when force bunching plays a significant role in the bunching process. A physical explanation for these findings is presented.

Much attention has been given in the past to two classes of squeezed states: the squeezed vacuum and coherent states. Here we study the effects of squeezing on number states and on thermal field states. The statistical properties of these various squeezed states are discussed using the second-order correlation functions. The quasiprobabilities of the Wigner, Q, and positive P representations are calculated and compared for the squeezed states. The Glauber P representation for the squeezed thermal state explicitly shows the limit of its applicability. The photon number distributions of the squeezed number and squeezed thermal states are extensively discussed and new interference effects in phase space are shown to lead to highly structured number distributions.

Squeezing of the atomic dipole moment in the one-photon and two-photon Jaynes-Cummings model is investigated with different initial conditions. Almost perfect squeezing is found in certain cases.

A method to calculate amplitudes for ionization in a strong laser field is developed that is constrained in such a way that gauge invariance is necessarily satisfied when approximations are introduced. A variational approximation procedure is adopted here, in the context of a simplified model of a charged particle bound in a short-range potential. The physical situation considered in an illustration of the method is one in which the external field is slowly varying relative to the time required for the particle to penetrate the potential barrier. The approximation derived here represents an extension of results obtained previously for problems of this type in that the effect of the laser field on the propagation of the particle during the ionization process is accounted for, in a manner consistent with the assumed slowly varying nature of the field. This is accomplished, specifically, through the replacement of the unperturbed propagator in the integral equation defining the continuum (momentum-space) wave function of the particle in the potential by a generalized Airy function. The relation between the approximation derived here and some results obtained previously is briefly discussed.

Dehmelt’s original idea of using the mechanism of quantum jumps for measurements is applied to the detection scheme of the dynamics of decay processes. The systems under consideration are the single atom inside a resonant optical cavity (waveguide) or the single trapped atom (ion) illuminated by the ionizing radiation. In each of the above cases the dark-period statistics of the side-level fluorescence is calculated and its specific features are pointed out.

We consider a single three-level atom placed inside a resonant cavity and simultaneously probed in a double-resonance ladder configuration by a relatively strong laser beam. It is shown that photocounting statistics of a fluorescence signal induced by the probe, in certain circumstances, exhibits dark periods (i.e., quantum jumps are present), reflecting the statistical properties of the field inside the cavity. Comparisons are made between the number, thermal, coherent, and squeezed states. Specific features of the latter are pointed out.

Sequences of coherent and squeezed pulses incident upon an inhomogeneously broadened two-level medium are examined and found to yield new forms of photon echoes. These echoes do not require a second coherent pulse to initiate the rephasing process. Rather, they are a consequence of the two different transverse atomic relaxation rates that exist for the duration of the squeezed pulse. These echoes suggest new ways of detecting and measuring squeezed light and of examining relaxation processes.

We apply recent developments in the study of singular Hopf bifurcations to describe the complete bifurcation diagram of a simple NMR laser with an injected signal. The branch of periodic solutions appears at a Hopf bifurcation point and may or may not disappear at a homoclinic point. The bifurcation is always subcritical, which suggests that the periodic solutions are all unstable. Our asymptotic analysis is based on the relative values of the fixed parameters in the problem. Our results complement earlier investigations by Holzner et al. [Phys. Rev. A 36, 1280 (1987)] and by Baugher, Hammack, and Lin [Phys. Rev. A 39, 1549 (1989)] on the subcritical Hopf bifurcation in a NMR laser.

Light scattering and interferometry techniques are used to demonstrate the influence of wetting phenomena on the stability of silica colloids when immersed in a homogeneous two-component fluid (2,6-lutidine and water). A reversible flocculation is observed for both fused quartz and Stöber silica particles. Its location in the fluid phase diagram is different according to the origin of the particles and corresponds only to the ‘‘wetting’’ side of the coexistence curve. The flocculation is preceded by the growth of adsorption layers whose composition is that of the expected wetting phase. A number of mechanisms, related to wetting transitions, that can explain these observations are discussed.

A series of direct-drive laser-fusion implosion experiments was performed on cryogenically cooled, DT-filled glass microballoons with the OMEGA 24-beam uv (351-nm) laser system. The targets consisted of glass microballoons having radii of 100 to 150 μm, wall thicknesses of 3 to 7 μm, filled with DT gas at pressures of 75 to 100 atm. The targets were cooled to below the freezing point of DT, in situ, by a cryogenic target system. The targets were irradiated by approximately 1 to 1.2 kJ of uv light in 650-ps Gaussian pulses. The on-target irradiation uniformity was enhanced for these experiments by the use of distributed phase plates, which brought the estimated irradiation nonuniformities to ∼12% (${\sigma }_{\mathrm{rms}}$). Target performance was diagnosed by an array of x-ray, plasma, and nuclear instruments. The measured target performance showed ∼70% absorption, thermonuclear yields of ${10}^6$ to ${10}^8$ neutrons, and final fuel areal densities of 20 to 40 mg/${\mathrm{cm}}^2$ for the optimum targets examined in these experiments. Fuel densities at the time of thermonuclear neutron production, inferred from direct measurements of the fuel areal density, were in the range of 20 to 50 g/${\mathrm{cm}}^3$ (100 to 200 times the density of liquid DT) for the optimum targets.

Experiments have been performed with the moderately intense electron-beam pulses (8 kA/${\mathrm{cm}}^2$ peak) at the Los Alamos National Laboratory pulsed high-energy radiographic machine emitting x-rays (PHERMEX) facility and with the much weaker beam at the Naval Research Laboratory linac, to measure energy absorption in Al, Ti, and W targets. The energy spectra at the two facilities were similar, with an average energy of about 26 MeV. A calorimetric method was used to measure the deposited energy. The experimental results are compared to each other and to Monte Carlo integrated ‘‘tiger’’ system (ITS) code calculations. Calorimeters consisting of two and four sections were used. The linac data were in good agreement with single-electron code calculations. Evidence for collective effects appears as a redistribution of the absorbed energy in the PHERMEX data, although the beam intensity is very much lower than in previous investigations of this effect.

This paper reports on studies of wetting phase behavior and interfacial density profiles of square-well fluid adsorbed at a square-well wall. At a specific drying transition, a comparison is made between computer-simulation data and coarse-grained density-functional theory. The successes and failures of this comparison form the basis of a detailed discussion of the strengths and weaknesses of the two approaches, as presently implemented, and proposals are made for removing the current ambiguities. In addition, density-functional theory is used to map out the global interfacial phase behavior at bulk liquid-vapor coexistence, in terms of the fields {T,${\epsilon }_w$} where T denotes temperature and ${\epsilon }_w$ is the strength of the attractive wall-fluid interaction. Particular attention is paid to questions of statistical-mechanical consistency in the form of exact sum rules.

Particle transport and mixing in modulated traveling waves in a binary-fluid mixture heated from below is studied numerically. The fluid divides into three regions separated by Kolmogorov-Arnol’d-Moser curves: a core region where particles are carried along with the wave (trapped), an outer region where particles are left behind by the wave (untrapped), and a separatrix layer between the two where particles chaotically alternate between being trapped and untrapped. The probability distributions for the lengths of individual trapped and untrapped events are sharply peaked at small times, have a power-law decay, and exhibit similar complex structure. The core and outer regions are responsible for long-range transport with no diffusion. The chaotic separatrix layer gives rise to long-range transport with enhanced mixing and anomalous diffusion, where, for long times 〈$x^2$(t)〉-〈x(t)${〉}^2$∼$t^{\nu }$, 1<ν<2.

In order to simulate viscous fingering in a porous medium with inhomogeneous permeability, we make use of a generalization of the diffusion-limited aggregation (DLA) model. In this generalized DLA, the randomly diffusing particles have transition probabilities which depend on the local permeability values of the underlying medium. This method is applied to the simulation of unstable two-fluid displacement in two-dimensional disordered pore-pipe networks. We show that the model may only be used to simulate flow in media which have inhomogeneous permeability and homogeneous porosity. We explore the combined effects of two types of noise: noise in the growth process, and disorder in the permeability of the medium; we find a morphology phase diagram which shows that both types of noise strongly affect morphology selection. In addition, we perform an analysis of DLA with noise reduction and find that the magnitude of interface velocity fluctuations is proportional to 1/√s , where s is the noise-reduction parameter. We show that these fluctuations are ‘‘multiplicative’’ in character and vanish in the large-noise-reduction limit. Finally, we address the potential application of this model to petroleum reservoir simulation.

Yomosa’s model for peptide chains is generalized in two respects. (1) The internal vibrations of the peptide groups are incorporated by considering a one-dimensional lattice with alternating masses and alternating linear and nonlinear interactions for the intrapeptide bonds and the hydrogen bonds between the peptide groups, respectively. (2) Discreteness effects are taken into account by applying a new version of Collin’s quasicontinuum approach. In the cases in which this approach is not sufficient, we apply an iterative method where the accuracy can be increased systematically. We obtain very narrow solitons with lower and upper velocity limits. Our results have been confirmed by computer simulations. The lifetime of the solitons is finite due to the emission of optical phonons. However, using α-helix parameters, this effect is negligible.