We consider a large class of optical cavities and gain media with an off-axis external feedback which introduces a two-point nonlocality. This nonlocality moves the lasing threshold and opens large windows of control parameters where weak light spots can be strongly amplified while the background radiation remains very low. Furthermore, transverse phase and group velocities of a signal can be independently tuned and this enables us to steer it nonmechanically, to control its spatial chirping, and to split it into two counterpropagating ones.

It is well recognized that the transmittance of Anderson localized systems decays exponentially on average with sample size, showing large fluctuations brought up by extremely rare occurrences of necklaces of resonantly coupled states, possessing almost unity transmission. We show here that in a one-dimensional (1D) random photonic system with resonant layers these fluctuations appear to be very regular and have a period defined by the localization length $\xi$ of the system. We stress that necklace states are the origin of these well-defined oscillations. We predict that in such a random system efficient transmission channels form regularly each time the increasing sample length fits so-called optimal-order necklaces and demonstrate the phenomenon through numerical experiments. Our results provide new insight into the physics of Anderson localization in random systems with resonant units.

We demonstrate that, in contrast with the well-studied photonic crystals consisting of two homogeneous components, photonic crystals comprised of inhomogeneous or multiple (three or more) components may bring new opportunities to photonics due to the discovered quasiperiodic resonant behavior of their ($hkl$) stop bands as a function of the reciprocal lattice vector. A resonant stop band cannot be switched off for any permittivity of structural components. Tuning the permittivity or structural parameters allows the selective on-off switching of nonresonant ($hkl$) stop bands. This independent manipulation of light at different Bragg wavelengths provides a new degree of freedom to design selective optical switches and waveguides. Transmission experiments performed on synthetic opals confirmed the theoretical predictions.

An approach is presented for extracting phase equations from multivariate time series data recorded from a network of weakly coupled limit cycle oscillators. Our aim is to estimate important properties of the phase equations including natural frequencies and interaction functions between the oscillators. Our approach requires the measurement of an experimental observable of the oscillators; in contrast with previous methods it does not require measurements in isolated single or two-oscillator setups. This noninvasive technique can be advantageous in biological systems, where extraction of few oscillators may be a difficult task. The method is most efficient when data are taken from the nonsynchronized regime. Applicability to experimental systems is demonstrated by using a network of electrochemical oscillators; the obtained phase model is utilized to predict the synchronization diagram of the system.

The propagation of bulk polaritons in ferromagnetic slab is considered through a short-wavelength approximation. Neither the damping nor the demagnetizing field do affect essentially the propagation and stability of the line soliton. The stable line soliton may be destroyed by background instability: the latter is suppressed in a narrow strip. The unstable line soliton decays into lumps, which can be described both numerically and through a variational approach. Lump interactions are mentioned.

This study is devoted to the experimental analysis of the stratorotational instability (SRI). This instability affects the classical cylindrical Couette flow when the fluid is stably stratified in the axial direction. In agreement with recent theoretical and numerical analyses, we describe for the first time in detail the destabilization of the stratified flow below the Rayleigh line (i.e., the stability threshold without stratification). We confirm that the unstable modes of the SRI are nonaxisymmetric, oscillatory, and take place as soon as the azimuthal linear velocity decreases along the radial direction. This new instability is relevant for accretion disks.

Dramatic enhancement of optical-field-ionization collisional-excitation x-ray lasing is achieved by using an optically preformed plasma waveguide. With a 9-mm-long pure krypton plasma waveguide prepared by using the axicon-ignitor-heater scheme, lasing at 32.8 nm is enhanced by 400 folds relative to the case without the plasma waveguide. An output level of $8\times {10}^{10}\mathrm{\text{photon}}/\mathrm{\text{shot}}$ is reached at an energy conversion efficiency of $2\times {10}^{-6}$. The same method is used to achieve x-ray lasing in a gas jet for the high-threshold low-gain transition at 46.9 nm in neonlike argon.

We show both theoretically and experimentally that biphoton wave packets generated via spontaneous parametric down-conversion can be strongly anisotropic and highly entangled. The conditions under which these effects exist are found and discussed.

We show that while the statistics of static speckle patterns are generic, fluctuations in the change within speckle patterns are greatly enhanced in the localization transition. The probability distributions of the displacement of phase singularities and the standard deviations of the changes of phase and intensity with frequency shift of incident microwave radiation are given in terms of the same expression which describes the probability distribution of total transmission. This function depends only upon a single parameter, the variance of the corresponding variable. The changing statistics in the localization transition reflects the number of underlying electromagnetic modes with which the incident wave interacts.

We establish analytically the interactions of electromagnetic wave with a general class of spherical cloaks based on a full wave Mie scattering model. We show that for an ideal cloak the total scattering cross section is absolutely zero, but for a cloak with a specific type of loss, only the backscattering is exactly zero, which indicates the cloak can still be rendered invisible with a monostatic (transmitter and receiver in the same location) detection. Furthermore, we show that for a cloak with imperfect parameters the bistatic (transmitter and receiver in different locations) scattering performance is more sensitive to ${\eta }_t=\sqrt{{\mu }_t/{ϵ}_t}$ than $n_t=\sqrt{{\mu }_t{ϵ}_t}$.

We study interactions of planetary waves propagating across the equator with trapped Rossby or Yanai modes, and the mean flow. The equatorial waveguide with a mean current acts as a resonator and responds to planetary waves with certain wave numbers by making the trapped modes grow. Thus excited waves reach amplitudes greatly exceeding the amplitude of the incoming wave. Nonlinear saturation of the excited waves is described by an amplitude equation with one or two attracting equilibrium solutions. In the latter case spatial modulation leads to formation of characteristic defects in the wave field. The evolution of the envelopes of long trapped Rossby waves is governed by the driven complex Ginzburg-Landau equation, and by the damped-driven nonlinear Schrödinger equation for short waves. The envelopes of the Yanai waves obey a simple wave equation with cubic nonlinearity.

Scaling laws of second-harmonic generation (SHG) in nonlinear Bragg stacks (or finite one-dimensional photonic crystals) as a function of the number $N$ of periods are explored. While it is known that SHG scales like the sixth power of $N$ when phase matching is achieved, we find maximal scaling like the eighth power of $N$ under appropriate non-phase-matching conditions with the pump and harmonic waves being resonant with band-edge states. In this framework we introduce the concept of self-adaptive coherence length that scales with the system length. An analytical treatment based on coupled-mode equations clarifies the conditions for obtaining different scaling laws as a function of filling factor in the photonic gap map.

We show that tapered arrays of thin metallic wires can manipulate electromagnetic fields on the subwavelength spatial scale. Two types of nanoscale imaging applications using terahertz and midinfrared waves are enabled: image magnification and radiation focusing. First, the tapered wire array acts as a multipixel TEM endoscope by capturing an electromagnetic field profile created by deeply subwavelength objects at the endoscope’s tip and magnifying it for observation. Second, the image of a large mask at the endoscope’s base is projected onto a much smaller image at the tip.

We present a dramatic enhancement [Phys. Rev. Lett. 91, 043002 (2003)] of high-order harmonic generation by simultaneous irradiation of booster harmonics. A key feature of our experiment is the use of mixed gases (Xe and He) with different ionization energies. The harmonics from Xe atoms act as a booster to increase the harmonic yield from He by a factor of $4\times {10}^3$. The dominance of the dramatic enhancement effect is supported by simulation with the time-dependent Schrödinger equation as well as the observed spatial characteristic of the generated harmonics and dependence on medium conditions.

We investigate the complexity of the dynamics of two mutually coupled systems with internal delays and vary the coupling delay over 4 orders of magnitude. Karhunen-Loève decomposition of spatiotemporal representations of fiber laser intensity data is performed to examine the eigenvalue spectrum and significant orthogonal modes. We compute the Shannon information from the eigenvalue spectra to quantify the dynamical complexity. A reduction in complexity occurs for short coupling delays while a logarithmic growth is observed as the coupling delay is increased.

We predict that modified thermal emission can result from three-dimensional, self-assembled photonic crystals. In previous tungsten structures, known as inverse opals, strong absorption prevented any influence of the periodicity. We consider the origin of this effect and show how to tailor both absorption and surface coupling in experimentally realizable metallic inverse opals. Calculations for tungsten, molybdenum, and tantalum crystals show that their optical properties can be similar to or even better than the tungsten woodpile, where modified thermal emission has already been seen.

An experimental study of a turbulent von Kármán flow in a cylinder is presented. The mean flow is stationary up to a Reynolds number $\mathrm{Re}={10}^4$ where a bifurcation takes place. The new regime breaks some symmetries of the problem and becomes time dependent because of equatorial vortices moving with a precession movement. In the exact counterrotating case, a bistable regime appears and spontaneous reversals of the azimuthal velocity are registered. A three-well potential model with additive noise reproduces this dynamic. A regime of periodic response is observed when a very weak forcing is applied.

We determine the intrinsic longitudinal dispersivity $l_d$ of randomly packed monodisperse spheres by separating the intrinsic stochastic dispersivity $l_d$ from dispersion by unavoidable sample dependent flow heterogeneities. The measured $l_d$, scaled by the hydrodynamic radius $r_h$, coincide with theoretical predictions [Saffman, J. Fluid Mech. 7, 194 (1960)] for dispersion in an isotropic random network of identical capillaries of length $l$ and radius $a$, for $l/a=3.82$, and with rescaled simulation results [Maier et al., Phys. Fluids 12, 2065 (2000)].

We propose a new technique for phase matching high harmonic generation that can be used for generating bright, tabletop, tunable, and coherent x-ray sources at keV photon energies. A weak quasi-cw counterpropagating field induces a sinusoidal modulation in the phase of the emitted harmonics that can be used for correcting the large plasma-induced phase mismatch. We develop an analytical model that describes this grating-assisted x-ray phase matching and predicts that very modest intensities ($<{10}^{10}\mathrm{W}/{\mathrm{cm}}^2$) of quasi-cw counterpropagating fields are required for implementation.

When a capillary is inserted into a liquid, the liquid will rapidly flow into it. This phenomenon, well studied and understood on the macroscale, is investigated by molecular dynamics simulations for coarse-grained models of nanotubes. Both a simple Lennard-Jones fluid and a model for a polymer melt are considered. In both cases after a transient period (of a few nanoseconds) the meniscus rises according to a $(\mathrm{\text{time}}{)}^{1/2}$ law. For the polymer melt, however, we find that the capillary flow exhibits a slip length $\delta$, comparable in size with the nanotube radius $R$. We show that a consistent description of the imbibition process in nanotubes is only possible upon modification of the Lucas-Washburn law which takes explicitly into account the slip length $\delta$. We also demonstrate that the velocity field of the rising fluid close to the interface is not a simple diffusive spreading.