The authors introduce a general mechanism, based on electrostatic and magnetostatic considerations, for designing three-dimensional isotropic metamaterials that possess an enhanced refractive index over an extremely large frequency range. The mechanism allows nearly independent control of effective electric permittivity and magnetic permeability without the use of resonant elements.

The effects of spin-induced gain anisotropy on output polarization and threshold current reduction of electrically pumped spin-polarized lasers have been studied. Analytical forms of these parameters are derived by considering diffusive transport from the spin injector to the active region. The calculated values of the parameter are in excellent agreement with values obtained from measurements made at 200 K on an $\mathrm{InAs}/\mathrm{GaAs}$ quantum dot spin-polarized vertical cavity surface-emitting laser. Electrical modulation of the output polarization of the laser is demonstrated with a peak modulation index of 0.6.

We show with numerical computation and analysis that Bloch waves, at either the center or edge of the Brillouin zone, of a one dimensional nonlinear periodic system can be regarded as infinite chains composed of fundamental gap solitons (FGSs). This composition relation between Bloch waves and FGSs leads us to predict that there are $n$ families of FGSs in the $n$th band gap of the corresponding linear periodic system, which is confirmed numerically. Furthermore, this composition relation can be extended to construct a class of solutions similar to Bloch waves but with multiple periods.

We establish a fundamental relationship between the averaged local density of states and the extinction mean free path of waves propagating in random media. From the principle of causality and the Kramers-Kronig relations, we show that both quantities are connected by dispersion relations and are constrained by a frequency sum rule. The results should be helpful in the analysis of wave transport through complex media and in the design of materials with specific transport properties.

We study the two-dimensional (2D) stochastic Navier-Stokes (SNS) equations in the inertial limit of weak forcing and dissipation. The stationary measure is concentrated close to steady solutions of the 2D Euler equations. For such inertial flows, we prove that bifurcations in the flow topology occur either by changing the domain shape, the nonlinearity of the vorticity–stream-function relation, or the energy. Associated with this, we observe bistable behavior in SNS with random changes from dipoles to unidirectional flows. The theoretical explanation being very general, we infer the existence of similar phenomena in experiments and in some regimes of geophysical flows.

We analyze the effect of porosity in a porous medium on hydrodynamic instabilities in reaction-diffusion fronts. We use an experimental device to create an effective two-dimensional porous medium which is vertically orientated. In this system the molecular diffusion coefficients and the acid autocatalysis of the chlorite-tetrathionate reaction satisfy the appropriate conditions to produce a chemical front that advances through the cell leading to the products overlaying the reactants. The reactants have a lower density than the products and therefore a buoyantly unstable front develops. To evaluate the influence of the porosity on the formation and propagation of such instabilities, media with different porosities were used in the experiments. The amplitude of the instability is found to reduce as the porosity of the medium is decreased. For sufficiently small porosity, the instability can almost disappear leading to a planar front.

We present an experimental study of the global velocity $V(t)$ of a viscous fluid interface during forced-flow imbibition in a disordered medium. Our high resolution setup shows that the fronts display an intermittent behavior signature of a burstlike dynamics, with power-law distributed avalanches. When measured at scales comparable to the correlation length, velocity fluctuations follow an asymmetric non-Gaussian distribution, whose skewness increases with decreasing measuring window and/or injection flow rate, offering the effective number of degrees of freedom probed in our experiment.

Nonlinearity in finite-Reynolds-number flow results in particle migration transverse to fluid streamlines, producing the well-known “tubular pinch effect” in cylindrical pipes. Here we investigate these nonlinear effects in highly confined systems where the particle size approaches the channel dimensions. Experimental and numerical results reveal distinctive dynamics, including complex scaling of lift forces with channel and particle geometry. The unique behavior described in this Letter has broad implications for confined particulate flows.

Based on the concept of complementary media, we propose an invisibility cloak operating at a finite frequency that can cloak an object with a prespecified shape and size within a certain distance outside the shell. The cloak is comprised of a dielectric core and an “antiobject” embedded inside a negative index shell. The cloaked object is not blinded by the cloaking shell since it lies outside the cloak. Full-wave simulations in two dimensions have been performed to verify the cloaking effect.

Acoustic bubble-size distributions have been determined using a pulsed ultrasound method at different ultrasound powers and frequencies. It was observed that the mean bubble size increased with increasing acoustic power and decreased with increasing ultrasound frequency. It was also recognized that the mean size of bubbles emitting sonoluminescence was greater than those producing sonochemiluminescence indicating that the two processes take place in different populations of cavitation bubbles in the system.

We investigate the propagation of a dark beam in a defocusing medium in the strong nonlinear regime. We observe for the first time a shock fan filled with noninteracting one-dimensional gray solitons that emanates from a gradient catastrophe developing around a null of the optical intensity. This scenario turns out to be very robust, persisting also when the material nonlocal response averages the nonlinearity over dimensions much larger than the emerging soliton filaments.

The singular values distribution of the propagation operator in a random medium is investigated in a backscattering configuration. Experiments are carried out with pulsed ultrasonic waves around 3 MHz, using an array of transducers. Coherent backscattering and field correlations are taken into account. Interestingly, the distribution of singular values shows a dramatically different behavior in the single and multiple-scattering regimes. Based on a matrix separation of single and multiple-scattered waves, an experimental illustration of imaging through a highly scattering slab is presented.

Microfluidic crystals are assemblies of miniature bubbles or drops flowing in channels. We explore here the flow of these crystals, when submitted to a given driving pressure. The flow velocity is linked to the finite number of elements in the channel width, and presents discontinuities when the crystal structure changes. At the transition from one structure to the other original dynamic features appear. The flow can self-regulate itself on a fixed velocity whatever the driving pressure, or, on the contrary, can spontaneously pulsate. All these features are predicted by simply considering the crystal’s energy and friction, and looking at the propagation of structure rearrangements. We anticipate these results to improve the control over the structure of dense two-phase flows in microfluidic systems.

We investigate mode-locking processes in lasers displaying a variable degree of structural randomness. By a spin-glass theoretic approach, we analyze the mean-field Hamiltonian and derive a phase diagram in terms of pumping rate and degree of disorder. Paramagnetic (noisy continuous wave emission), ferromagnetic (standard passive mode locking), and spin-glass phases with an exponentially large number of configurations are identified. The results are also relevant for other physical systems displaying a random Hamiltonian, such as Bose-condensed gases and nonlinear optics.

We perform an accurate polarimetry measurement of high-order harmonic emission from aligned molecules. We find that harmonic emission from ${\mathrm{N}}_2$ can be strongly elliptically polarized even when driven by linearly polarized laser fields. These data have broad implications for understanding molecules in strong fields because they cannot be explained by simple theories based on the strong field approximation and single active electron models. Finally, this work also shows that it is possible to engineer the polarization properties of harmonic emission by carefully preparing a molecular medium.

Periodic spatial intensity modulations of near-band-gap luminescence light at 3.36 eV photon energy are reported in nanometer-sized resonators of single zinc oxide nanorods. These modulations are observed when the luminescence light, due to excitonic recombination, is excited by a focused low-energy electron beam scanned along the rods. The acceleration energy of only 2 keV allows for a spatial resolution of a few ten nanometers. Numerical calculations based on the theory of dielectric cylindrical waveguides are performed identifying the intensity modulations as beating patterns of coupled ${\mathrm{TE}}_{01}$ and ${\mathrm{TM}}_{01}$ modes in the nanoresonator.

We report an optical interference experiment which seems to contradict our common knowledge, in that the formation of the interference pattern originates from a spatially incoherent light source. Our experimental scheme is very similar to Gabor’s original proposal of holography [Nature (London) 161, 777 (1948)], except that an incoherent source replaces the coherent one. Though an instantaneous interference pattern between an object wave and reference wave fluctuates irregularly, a well-defined pattern appears in the statistical average, in accord with a hologram in the coherent light case.

In this Letter, we report for the first time on the experimental observation of the generalized synchronization regime in the microwave electronic systems, namely, in the multicavity klystron generators. A new approach devoted to the generalized synchronization detection has been developed. The experimental observations are in the excellent agreement with the results of numerical simulation. The observed phenomena gives a strong potential for new applications requiring microwave chaotic signals.

Using covariant Lyapunov vectors, we reveal a split of the tangent space of standard models of one-dimensional dissipative spatiotemporal chaos: A finite extensive set of $N$ dynamically entangled vectors with frequent common tangencies describes all of the physically relevant dynamics and is hyperbolically separated from possibly infinitely many isolated modes representing trivial, exponentially decaying perturbations. We argue that $N$ can be interpreted as the number of effective degrees of freedom, which has to be taken into account in numerical integration and control issues.

We used ultrafast x radiography and developed a novel multiphase numerical simulation to reveal the origin and the unique dynamics of the liquid-jet-generated shock waves and their interactions with the jets. Liquid-jet-generated shock waves are transiently correlated to the structural evolution of the disintegrating jets. The multiphase simulation revealed that the aerodynamic interaction between the liquid jet and the shock waves results in an intriguing ambient gas distribution in the vicinity of the shock front, as validated by the ultrafast x-radiography measurements. The excellent agreement between the data and the simulation suggests the combined experimental and computational approach should find broader applications in predicting and understanding dynamics of highly transient multiphase flows.