The spectral response of a monolithic semiconductor quantum microcavity with quantum wells as the active medium displays mode splitting when the quantum wells and the optical cavity are in resonance. This effect can be seen as the Rabi vacuum-field splitting of the quantum-well excitons, or more classically as the normal-mode splitting of coupled oscillators, the excitons, and the electromagnetic field of the microcavity. An exciton oscillator strength of 4×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$ is deduced for 76-Å quantum wells.

We show experimental evidence of extremely low thresholds for subharmonic generation of ultrasonic waves in one-dimensional artifical piezoelectric plates with Cantor-like structure, as compared to the corresponding homogeneous and periodical plates. The origin of this apparent anomaly is theoretically investigated by studying anharmonic coupling between normal modes. We demonstrate that the large enhancement of nonlinear interaction results from the more favorable frequency and spatial matching of coupled modes (fractons and phonons) in the Cantor-like structure, with no need to invoke anomalous modifications of the nonlinear elastic constants.

It is shown that the unstable steady state of a multimode laser system may be stabilized by the occasional proportional feedback technique for dynamical control of chaotic systems. The range of pump excitations over which stabilization can be maintained is extended by more than an order of magnitude through application of a procedure for tracking the unstable steady state as the pump excitation is slowly varied.

It is shown that an inverse cascade of the turbulence of inertio-gravity waves produces a long-scale wave condensate. A new nonlinear equation is derived for long waves on rotating shallow water. It is proven that steady localized solutions are absent and that the condensate (a uniform inertial oscillation) is stable with respect to small perturbations. Wave self-interaction could not thus stop an inverse cascade of mesoscale geophysical turbulence. The implication of the existence of a condensate for the problem of tidal dissipation and retardation of the Earth’s rotation is discussed.

We report, for the first time, the experimental observation of solitary waves in an axisymmetric Taylor-Couette flow. The solitary waves result from a parity-breaking bifurcation which occurs near the onset of Eckhaus instability for Taylor vortex flow in a wide-gap, counterrotating system (radius ratio η=0.5 and speed ratio μ=-0.2). Our results agree quantitatively with a recent theoretical calculation by Riecke and Paap.

The current generation of photon scattering experiments requires a fast, accurate, general technique for calculation of transmission coefficients and of photonic band structure. A new methodology, which has significant advantages of speed and convenience, enables the band structure and, for the first time, transmission coefficients of complex dielectric materials to be calculated. Excellent agreement with experiment is found.

In previous works we have defined statistical equilibrium states for two-dimensional incompressible Euler equations. We establish here evolution equations governing the relaxation of the system towards these equilibrium states.

It is shown that signed measures (i.e., measures that take on both positive and negative values) may exhibit an extreme form of singularity in which oscillations in sign occur everywhere on arbitrarily fine scale. A cancellation exponent is introduced to characterize such measures quantitatively, and examples of significant physical situations which display this striking type of singular behavior are discussed.

Experiments are performed which illustrate the properties of damped traveling waves in diffusive media. Our observations demonstrate the manipulation of these waves by adjustment of the photon diffusion coefficients of adjacent turbid media. The waves are imaged, and are shown to obey simple relations such as Snell’s law. The extent to which analogies from physical optics may be used to understand these waves is further explored, and the implications for medical imaging are briefly discussed.

Exchange of angular momentum between photons and atoms cannot only cause optical pumping, but also a lateral displacement of a laser beam traveling through a homogeneous atomic vapor. We present experimental data from the ground state of atomic sodium demonstrating this effect.

The transition to turbulence in plane Couette flow was studied experimentally. The subcritical aspect of this transition is revealed by the stable coexistence of laminar and turbulent domains. By perturbing the flow, a critical Reynolds number has been determined, above which an artificially triggered turbulent spot can persist. The study of the spatiotemporal evolution of these spots shows, among other things, the existence of waves traveling away from the turbulent regions.

Rotating convection near onset is studied using a three mode model but with the inclusion of spatial dependence. An apparently chaotic dynamics is found, consistent with experiment, without the necessity of adding ad hoc noise terms as in previous models. There is no phase transition approaching the point of linear instability of straight rolls from the disordered side, and the characteristic domain size and switching time remain finite here. This behavior is discussed in terms of the velocity of walls between the different domains.

I report observations of a new state of traveling-wave convection which consists of pairs of localized wave packets which propagate around an annular cell in opposite directions. During their periodic collisions, the wave packets experience a loss in amplitude due to nonlinear interaction which exactly compensates the linear gain they experience at other times. This leads to a regular, small-amplitude state with high phase and group velocities. This state offers the promise of being quantitatively explainable on first principles using the simplest model of coupled complex Ginzburg-Landau equations.

We have investigated the properties of light emitted into the nearest subthreshold mode on either side of the single lasing mode of an argon-ion laser. This light beats with the laser line and hence contributes to the laser’s intensity-fluctuation noise spectrum over a range of frequencies centered close to the longitudinal mode separation. The noise contribution from one subthreshold mode is shown to be strongly anticorrelated with that from the other, leading to optical noise cancellation.

A new spectroscopy based on the resonant coherently induced electron loss to the continuum in ion-surface scattering under grazing incidence is proposed. A series of peaks, corresponding to the energy differences determined by the resonant interaction with the rows of atoms in the surface, is predicted to appear in the energy distribution of electrons emitted from electronic states bound to the probe. Calculations for MeV ${\mathrm{He}}^{+}$ ions scattered at a W(001) surface along the 〈100〉 direction with a glancing angle of 0–2 mrad show a total yield close to 1.

The transition from quasiperiodicity to chaos is studied in a two-dimensional dissipative map with the inverse-golden-mean rotation number. On the basis of a decimation scheme, it is argued that the (minimal) slope of the critical iterated circle map is proportional to the effective Jacobian determinant. Approaching the zero-Jacobian-determinant limit, the factor of proportion becomes a universal constant. Numerical investigation on the dissipative standard map suggests that this universal number could become observable in experiments.

We study the fluctuation properties of $0^{+}$ levels in rotational nuclei using the framework of SU(3) dynamical symmetry of the interacting boson model. Computations of Poincaré sections for SU(3) dynamical symmetry and its breaking confirm the expected relation between dynamical symmetry and classical chaos. On the other hand, the quantal energy level statistics in the realistic case of rotational nuclei is close to Gaussian-orthogonal-ensemble statistics, contrary to expectations. The conjectured relation between energy fluctuations and chaos is approached asymptotically. Several predictions for chaotic behavior of normally deformed and superdeformed rotational nuclei are given.

A class of strongly chaotic systems revealing a strange arithmetical structure is discussed whose quantal energy levels exhibit level attraction rather than repulsion. As an example, the nearest-neighbor level spacings for Artin’s billiard have been computed in a large energy range. It is shown that the observed violation of universality has its root in the existence of an infinite number of Hermitian operators (Hecke operators) which commute with the Hamiltonian and generate nongeneric correlations in the eigenfunctions.

Two intersecting laser beams of orthogonal circular polarization near resonant to the homogeneously broadened D1 transition of Na vapor were observed to deflect each other upon contact. The experimental results are in good agreement with calculations based on a model which includes diffraction and a local nonlinear atomic susceptibility wihch fully takes into account saturation and optical pumping effects. The contact deflection (or ‘‘bouncing’’) was also observed when both beams were tuned to the atomic resonance frequency.

An analytical model of three-dimensional Euler flows which exhibits a finite-time singularity is given. The singularity in vorticity occurs at a velocity field null (stagnation point) which lies on the line joining two vorticity field nulls. It is shown that the vorticity diverges inversely with time.