We examine the origin of diffuse gas-particle scattering by molecular dynamics simulation and show that diffuse scattering is the consequence of gas molecule trapping on the particle surface. Trapping occurs because of gas-particle interactions and the particle’s ability of energy accommodation. These observations explain the transition from specular-to-diffuse scattering as the particle size becomes larger than the molecular size. We discuss the implication of this transition on the transport properties of nanometer-size particles.

In many applications a sustained, localized turbulent flow scours a cohesionless granular bed to form a pothole. Here we use similarity methods to derive a theoretical formula for the equilibrium depth of the pothole. Whereas the empirical formulas customarily used in applications contain numerous free exponents, the theoretical formula contains a single one, which we show can be determined via the phenomenological theory of turbulence. Our derivation affords insight into how a state of dynamic equilibrium is attained between a granular bed and a localized turbulent flow.

Diffraction gratings affect the absolute phase of light in a way that is not obvious from the usual derivation of optical paths using the grating equation. For example, consider light which encounters first one and then the second of two parallel gratings. If one grating is moved parallel to its surface, the phase of the light diffracted from the grating pair is shifted by $2\pi$ each time the grating is moved by one grating constant, even though the geometric path length is not altered by the motion. This additional phase shift must be included when incorporating diffraction gratings in interferometers.

A new generalized nonlinear Schrödinger equation describing the propagation of ultrashort pulses in bulk media exhibiting frequency dependent dielectric susceptibility and magnetic permeability is derived and used to characterize wave propagation in a negative index material. The equation has new features that are distinct from ordinary materials ($\mu =1$): the linear and nonlinear coefficients can be tailored through the linear properties of the medium to attain any combination of signs unachievable in ordinary matter, with significant potential to realize a wide class of solitary waves.

We demonstrate that electromagnetic waves can transmit with unit transmittance through a slab of negative-permittivity media sandwiched between two identical slabs with high permittivity, although each single slab is nearly opaque. This type of transparency is accompanied by high magnetic fields, and is robust against incidence angles. Microwave experiments, in excellent agreement with finite-difference-time-domain simulations, are performed to successfully realize this idea.

We consider a large class of nonlinear diffusive systems with nonlocal coupling. By using a nonperturbative analytical approach we are able to determine the convective and absolute instabilities of all the uniform states of these systems. We find a huge window of convective instability that should provide a great opportunity to study experimentally and theoretically noise sustained patterns.

The relation between the fundamental parameters of energy and temporal duration of ultrashort pulses, under the condition of varying the average dispersion, are demonstrated both theoretically and experimentally in a solid-state femtosecond mode-locked laser. An asymptotic theory for nonlinear and dispersion managed solitons agrees well with the experimental data and demonstrates that the dominant factor in the pulse dynamics arises from the equilibrium established between the nonlinear Kerr effect and linear dispersion.

Bistability induced by the nonlinear Kerr effect in arrays of coupled waveguides is studied and shown to be a means to conceive light detectors that switch under excitation by a weak signal. The detector is obtained by coupling two single 1D waveguides to an array of coupled waveguides with adjusted indices and coupling. The process is understood by an analytical description in the conservative and continuous case and illustrated by numerical simulations of the model with attenuation.

We investigate the effect of classical singularities on the quantum properties of nonrandom Hamiltonians. A kicked rotator with a nonanalytical potential is discussed in detail. It is shown that classical singularities produce anomalous diffusion in the classical phase space. Quantum mechanically, the eigenstates of the evolution operator are power-law localized with an exponent given by the type of classical singularity. For logarithmic singularities, the classical motion presents $1/f$ noise and the quantum properties resemble those of an Anderson transition. Neither the classical nor the quantum properties depend on the details of the potential but only on the type of singularity. We thus define a new universality class in quantum chaos by the relation between classical singularities (anomalous diffusion) and quantum power-law localization.

Highly efficient high-harmonic generation was achieved in helium using a two-color laser field that consisted of the fundamental and the second harmonic fields of a femtosecond Ti:sapphire laser. By applying a high intensity second harmonic, the harmonics generated in the orthogonally polarized two-color field were stronger than those obtained in the fundamental field by more than 2 orders of magnitude, and even stronger than those of the parallel polarization case. A conversion efficiency as high as $5\times {10}^{-5}$ was obtained for the 38th harmonic at 21.6 nm. The physical origin of this enhancement was deduced by analyzing the electron behavior in the two-color field.

The evolution of infinitesimal, localized perturbations is investigated in a one-dimensional diatomic gas of hard-point particles (HPG) and thereby connected to energy diffusion. As a result, a Levy walk description, which was so far invoked to explain anomalous heat conductivity in the context of noninteracting particles is here shown to extend to the general case of truly many-body systems. Our approach does not only provide firm evidence that energy diffusion is anomalous in the HPG, but proves definitely superior to direct methods for estimating the divergence rate of heat conductivity which turns out to be $0.333\pm 0.004$, in perfect agreement with the dynamical renormalization-group prediction ($1/3$).

Using supersymmetry calculations and random matrix simulations, we study the decay of the average of the fidelity amplitude $f_{ϵ}(\tau )=⟨\psi (0)|\exp (2\pi i{H}_{ϵ}\tau )\exp (-2\pi i{H}_0\tau )|\psi (0)⟩$, where $H_{ϵ}$ differs from $H_0$ by a slight perturbation characterized by the parameter $ϵ$. For strong perturbations a recovery of $f_{ϵ}(\tau )$ at the Heisenberg time $\tau =1$ is found. It is most pronounced for the Gaussian symplectic ensemble, and least for the Gaussian orthogonal one. Using Dyson’s Brownian-motion model for an eigenvalue crystal, the recovery is interpreted in terms of a spectral analogue of the Debye-Waller factor known from solid state physics, describing the decrease of x-ray and neutron diffraction peaks with temperature due to lattice vibrations.

Using total internal reflection-fluorescence recovery after photobleaching, the local velocity, averaged over distances of 50 nm from the solid wall, has been measured for two different simple liquids, squalane and hexadecane, sheared on three smooth surfaces with similar roughness but with gradually decreasing fluid-solid interactions. We show that not only the strength of the fluid-solid interactions, but also the shape of the molecules of the fluid deeply affect the friction and the degree of slip at the wall.

Recently it has been demonstrated that spatial filtering of images in microscopy with a spiral phase element in a Fourier plane of the optical path results in a strong edge enhancement of object structures. In principle the operation is isotropic, i.e., all phase edges of a sample object are highlighted simultaneously, independent of their local direction. However, here we demonstrate that the symmetry can be broken intentionally by controlling the phase of the central area of a spiral phase hologram, which is displayed at a computer controlled spatial light modulator. This produces an apparent shadow effect which can be rotated at video rate. The resulting relieflike impression of the sample topography with a longitudinal resolution in the subwavelength regime is demonstrated by imaging a standard low contrast test sample consisting of a human cheek cell.

We describe the rich dynamic behavior—including period-doubling and period-halving bifurcations, intermittency, and chaos—observed in the breakup of an inviscid fluid in a coflowing, viscous liquid, both confined in a microfabricated flow-focusing geometry. Experimental observations support inertia-dominated dynamics of the interface, and suggest the possible similarity to the dynamics of a topologically inverted counterpart of this system, that is, a dripping faucet.

In a two-dimensional soap film convection experiment, the velocity fields are found to be strongly intermittent in the buoyancy subrange, which was reported to be nonintermittent in a recent numerical simulation. The structure functions $S_q(l)(=⟨|\delta v_l{|}^q⟩)$ exhibit self-similar structures and can be described by power laws $l^{\zeta q}$ for integers $8\ge q\ge 1$. By extending Kolmogorov’s refined similarity hypothesis to our system, an analytical form is derived for the scaling exponent ${\zeta }_q=q/2+(\mu /18)(3q-q^2)$. Our measurements yield $\mu =0.42$, which is significantly greater than 0.2 found in high Reynolds number turbulence in wind tunnels.

We report the onset of wave chaos in a real-world vertical-cavity surface-emitting laser. In a joint experimental and modeling approach we demonstrate that a small deformation in one layer of the complicated laser structure changes the emission properties qualitatively. Based on the analysis of the spatial emission profiles and spectral eigenvalue spacing distributions, we attribute these changes to the transition from regular behavior to wave chaos, and justify the full analogy to two-dimensional billiards by model calculations. Hence, these lasers represent fascinating devices for wave chaos studies.

We analyze experimentally and theoretically mechanical oscillation within an optical cavity stimulated by the pressure of circulating optical radiation. The resulting radio frequency cavity vibrations (phonon mode) cause modulation of the incident, continuous-wave (cw) input pump beam. Furthermore, with increasing cw pump power, an evolution from sinusoidal modulation to random oscillations is observed in the pump power coupled from the resonator. The temporal evolution with pump power is studied, and agreement was found with theory. In addition to applications in quantum optomechanics, the present work suggests that radiation-pressure-induced effects can establish a practical limit for the miniaturization of optical silica microcavities.

We report the controlled observation of the nonequilibrium Ising-Bloch transition in a broad area nonlinear optical cavity (a quasi-1D single longitudinal-mode photorefractive oscillator in a degenerate four-wave mixing configuration). Our experimental technique allows for the controlled injection of the domain walls. We use cavity detuning as control parameter and find that both Ising and Bloch walls can exist for the same detuning values within a certain interval of detunings; i.e., the Ising-Bloch transition is hysteretic in our case. A complex Ginzburg-Landau model is used for supporting the observations.

Experiments in the dynamic fracture of brittle polyacrylamide gels show that a single-crack state undergoes a hysteretic transition to the microbranching instability with a characteristic activation time. Quantitative measurements also indicate that features such as crack front inertia, self-focusing of microbranches, and the appearance of front waves are universal attributes of dynamic fracture.