We demonstrate that modulation instability leading to optical pattern formation can arise by using nonconventional counterpropagating beams carrying an orbital angular momentum (optical vortices). Such a vortex beam is injected into a nonlinear single feedback system. We evidence different complex patterns with peculiar phase singularities and rotating dynamics. We prove that the dynamics is induced by the vortex angular momentum and the rotation velocity depends nonlinearly on both the vortex topological charge and the intensity of the input beam.

Here we extend the reach of Fano resonant coupling by combining this concept with cloaking and plasmonic resonances in a single nonlinear nanoparticle, in order to realize giant all-optical scattering nanoswitches controlled by moderate pumping intensities. We show that a core-shell nonlinear plasmonic particle may be designed to abruptly switch from being completely cloaked to being strongly resonant, with up to a 40 dB cross-sectional difference. Self-tunable optical cloaks and resonant scatterers are envisioned for use as efficient all-optical switches and nanomemories.

We implement three photon fluorescence polarization resolved microscopy to optically investigate molecular and protein crystals. The availability of UV transitions using IR pulses allows analyses without fluorescence staining. Polarization resolved studies indicate that high-order symmetry structures can be revealed and that strong fluorescent energy transfer occurs between molecules. We show how this permits identification of a monocrystalline nature for a sample at the subwavelength resolution scale.

A novel method of producing intense short wavelength radiation from relativistic electrons is described. The electrons are periodically bunched at the wavelength of interest enabling in-phase superradiant emission that is far more intense than from unbunched electrons. The periodic bunching is achieved in steps beginning with an array of beamlets emitted from a nanoengineered field emission array. The beamlets are then manipulated and converted to a longitudinal density modulation via a transverse-to-longitudinal emittance exchange. Periodic bunching at short wavelength is shown to be possible, and the partially coherent x-ray properties produced by inverse Compton scattering from an intense laser are estimated. The proposed method increases the efficiency of x-ray production by several orders of magnitude, potentially enabling compact x-ray sources to produce brilliance and flux similar to major synchrotron facilities.

We present two powerful semiclassical formulas for quantum systems with classically chaotic dynamics, one of them being the Fourier transform of the other. The first formula evaluates the autocorrelation function of a state constructed in the neighborhood of a short periodic orbit, where the propagation for times greater than the Ehrenfest time is computed through the contribution of homoclinic orbits. The second formula evaluates the square of the overlap of the proposed state with the eigenstates of the system, providing valuable information about the scarring phenomenon. Both expressions are successfully verified in the Bunimovich stadium billiard.

We study the hydrodynamic interaction between a sphere and an elastic surface at a nanoscale with a dynamic surface force apparatus. We show that the interplay between viscous forces and elastic deformations leads to very rich scaling properties of the force response, providing a unique signature of the surface elastic behavior. These properties are illustrated on three different examples: a thick elastomer, a thin elastomer film, and a layer of micrometric bubbles. We show that this fluid probing allows one to measure the Young’s modulus of surfaces and soft thin layers at distance, without any direct solid-solid contact.

In this Letter we present a theoretical analysis of the droplet breakup with “permanent obstruction” in a microfluidic $T$ junction [M.-C. Jullien et al., Phys. Fluids 21, 072001 (2009)]. The proposed theory is based on a simple geometric construction for the interface shape combined with Tanner’s law for the local contact angle. The resulting scaling of the droplet deformation with time and capillary number is in excellent agreement with the results of direct numerical simulations and prior experiments. More rigorous analysis based on the lubrication approximation reveals a self-similar behavior analogous to the classical problem of a droplet spreading over a preexisting liquid film.

A walker is a classical self-propelled wave particle association moving on a fluid interface. Two walkers can interact via their waves and form orbiting bound states with quantized diameters. Here we probe the behavior of these bound states when setting the underlying bath in rotation. We show that the bound states are driven by the wave interaction between the walkers and we observe a level splitting at macroscopic scale induced by the rotation. Using the analogy between Coriolis and Lorentz forces, we show that this effect is the classical equivalent to Zeeman splitting of atomic energy levels.

We demonstrate the ultranarrow temporal correlation (6 fs full width half maximum) of twin beams generated by parametric down-conversion by using its reverse process, i.e., sum-frequency generation. The result relies on an achromatic imaging of a huge bandwidth of twin beams and on a careful control of their spatial degrees of freedom. The detrimental effects of spatial filtering and imperfect imaging are shown, along with the theoretical model used to describe the results.

In this Letter, we propose an original and novel experimental method to characterize both the onset and morphology of Taylor-Couette instability occurring in a non-Newtonian cylindrical Couette flow. Using synchrotron-based rheological small angle x-ray scattering experiments, we jointly investigate the shear-thinning behavior of natural swelling clays suspensions and the associated anisotropy developing in such media. Combined with a linear stability analysis for power law fluids, a destabilizing effect is shown both numerically and experimentally and the vortices morphology is found to be dependent on the fluid index. Still, the strong destabilizing effect and large vortex size can not be assigned to shear-thinning only, which clearly evidences the impact of medium anisotropy on Taylor-Couette instability.

Femtosecond-scale polarization state shaping is experimentally found in optical response of a plasmonic nanograting by means of time-resolved Stokes polarimetry. Simultaneous measurements of the Stokes parameters as a function of time reveal a remarkable alteration of the polarization state inside a single femtosecond pulse reflected from a plasmonic crystal due to the excitation of time-delayed polarization-sensitive surface plasmons with a highly birefringent Fano-type spectral profile. Time-dependent depolarization, indicating the sub-130-femtosecond polarization change inside the pulse, is experimentally found and described within an analytical model which predicts the fivefold enhancement of the polarization conversion effect with the use of a narrower time gate.

In wavelength-scale cavities with chiral-symmetric geometry, wave optical effects can introduce local chirality, that is, a spatial separation of the clockwise and counterclockwise propagating resonant modes. We show that this local chirality results in unidirectional lasing emission in the far field. In the presence of a waveguide, the local chirality also allows for directional evanescent coupling of the lasing modes, and the output direction can be varied by selecting the coupling position along the cavity boundary. Our results demonstrate that the local chirality of optical resonances can be utilized to control the output directionality and enhance the collection efficiency of emission from ultrasmall resonators.

Optical solitons or solitonlike states shed light to blueshifted frequencies through a resonant emission process. We predict a mechanism by which a second propagating mode is generated. This mode, called negative resonant radiation, originates from the coupling of the soliton mode to the negative-frequency branch of the dispersion relation. Measurements in both bulk media and photonic-crystal fibers confirm our predictions.

We demonstrate a robust and generic mechanism, which we term “chaos-assisted channeling,” to achieve unidirectional output from wave-chaotic microcavities with long-lived resonances. It utilizes the coexistence of regular and chaotic ray dynamics in most deformed microcavities. Long-lived resonances are formed by total internal reflection on classical periodic orbits, and their leakage into the chaotic region of the phase space is efficiently channeled into an attached waveguide without additional loss. We explain this behavior using a ray dynamics analysis which is confirmed via numerical simulations and experimental demonstration.

We report on the experimental demonstration of a hybrid optoelectronic neuromorphic computer based on a complex nonlinear wavelength dynamics including multiple delayed feedbacks with randomly defined weights. This neuromorphic approach is based on a new paradigm of a brain-inspired computational unit, intrinsically differing from Turing machines. This recent paradigm consists in expanding the input information to be processed into a higher dimensional phase space, through the nonlinear transient response of a complex dynamics excited by the input information. The computed output is then extracted via a linear separation of the transient trajectory in the complex phase space. The hyperplane separation is derived from a learning phase consisting of the resolution of a regression problem. The processing capability originates from the nonlinear transient, resulting in nonlinear transient computing. The computational performance is successfully evaluated on a standard benchmark test, namely, a spoken digit recognition task.

We study fluid flow at the interfaces between elastic solids with randomly rough, self-affine surfaces. We show by numerical simulation that elastic deformation lowers the relative contact area at which contact patches percolate in comparison to traditional approaches to seals. Elastic deformation also suppresses leakage through contacts even far away from the percolation threshold. Reliable estimates for leakage can be obtained by combining Persson’s contact mechanics theory with a slightly modified version of Bruggeman’s effective-medium solution of the Reynolds equation.

With enhancing mixing in micro- or nanofluidic applications in mind, the problem of maximizing fluid transport across a fluid interface subject to an available energy budget is examined. The optimum cross-interface perturbing velocity is obtained explicitly in the time-periodic instance using an Euler-Lagrange constrained optimization approach. Numerical investigations which calculate transferred lobe areas and cross-interface flux are used to verify that the predicted strategy achieves optimum transport. Explicit active protocols for achieving this optimal transport are suggested.

We find that electromagnetic waves can be guided at the edge of a three-dimensional photonic crystal in air. When the waveguide is defined by the intersection of two surface planes, the edge modes are associated with the corresponding surface bands. A simple cell counting approach is presented to describe the periodic evolution of the system with interesting interplays among edge, surface, and bulk states.

After recapitulating the covariant formalism of equilibrium statistical mechanics in special relativity and extending it to the case of a nonvanishing spin tensor, we show that the relativistic stress-energy tensor at thermodynamical equilibrium can be obtained from a functional derivative of the partition function with respect to the inverse temperature four-vector $\beta$. For usual thermodynamical equilibrium, the stress-energy tensor turns out to be the derivative of the relativistic thermodynamic potential current with respect to the four-vector $\beta$, i.e., $T^{\mu \nu }=-\partial {\Phi }^{\mu }/\partial {\beta }_{\nu }$. This formula establishes a relation between the stress-energy tensor and the entropy current at equilibrium, possibly extendable to nonequilibrium hydrodynamics.

In the current-driven, kink-type Tayler instability (TI) a sufficiently strong azimuthal magnetic field becomes unstable against nonaxisymmetric perturbations. The TI has been discussed as a possible ingredient of the solar dynamo mechanism and a source of the helical structures in cosmic jets. It is also considered as a size-limiting factor for liquid metal batteries. We report on a liquid metal TI experiment using a cylindrical column of the eutectic alloy GaInSn to which electrical currents of up to 8 kA are applied. We present results of external magnetic field measurements that indicate the transient occurrence of the TI in good agreement with numerical predictions. The interference of TI with the competing large-scale convection, resulting from Joule heating, is also discussed.