We demonstrate a technique for generating tunable all-optical delays in room temperature single-mode optical fibers at telecommunication wavelengths using the stimulated Brillouin scattering process. This technique makes use of the rapid variation of the refractive index that occurs in the vicinity of the Brillouin gain feature. The wavelength at which the induced delay occurs is broadly tunable by controlling the wavelength of the laser pumping the process, and the magnitude of the delay can be tuned continuously by as much as 25 ns by adjusting the intensity of the pump field. The technique can be applied to pulses as short as 15 ns. This scheme represents an important first step towards implementing slow-light techniques for various applications including buffering in telecommunication systems.

Utilizing single fluorescent molecules as probes, we prove the ability of a far-field microscope to attain spatial resolution down to 16 nm in the focal plane, corresponding to about $1/50$ of the employed wavelength. The optical bandwidth expansion by nearly an order of magnitude is realized by a saturated depletion through stimulated emission of the molecular fluorescent state. We demonstrate that en route to the molecular scale, the resolving power increases with the square root of the saturation level, which constitutes a new law regarding the resolution of an emerging class of far-field light microscopes that are not limited by diffraction.

We analyze the general features of the formation and interaction of transverse traveling waves and the appearance of filamentation in broad area semiconductor lasers with current profiling. For small apertures, the emitted profile is symmetric consisting of two counterpropagating transverse traveling waves, both emanating from the center of the device. For larger apertures, the emission becomes asymmetric as one of the traveling waves expands to occupy an increased area while the other occupies the remaining, smaller spatial region. In both devices, the pattern becomes unstable at higher injection currents due to optical filamentation, although an intermediate state is present in the wider device whereby the dominant wave undergoes a Hopf bifurcation before filamentation occurs.

Virtually all electromagnetic waveguiding structures support a multiplicity of modes. Nevertheless, to date, an experimental method for unique decomposition of the fields in terms of the component eigenmodes has not been realized. The fundamental problem is that all current attempts of modal decomposition do not yield phase information. Here we introduce a noninterferometric approach to achieve modal decomposition of the fields at the output of a general waveguiding structure. The technique utilizes a mapping of the two-dimensional field distribution onto the one-dimensional space of waveguide eigenmodes, together with a phase-retrieval algorithm to extract the amplitudes and phases of all the guided vectorial modes. Experimental validation is provided by using this approach to examine the interactions of 16 modes in a hollow-core photonic-band gap fiber.

We present visualization and measurement of the convection of water under a high magnetic field applied vertically to the fluid. The convection was either suppressed or enhanced depending on the direction of the magnetic force. The magnetic field effect was evaluated quantitatively by measuring the onset of convection, and discussed in terms of the Rayleigh number which includes the magnetic term. The results clearly show that the convection in a diamagnetic fluid such as water can be controlled using a common 10 T class magnet.

We quantify the presence of direct processes in the $S$ matrix of chaotic microwave cavities with absorption in the one-channel case. To this end the full distribution $P_S(S)$ of the $S$ matrix, i.e., $S=\sqrt{R}{e}^{i\theta }$, is studied in cavities with time-reversal symmetry for different antenna coupling strengths $T_a$ or direct processes. The experimental results are compared with random-matrix calculations and with numerical simulations including absorption. The theoretical result is a generalization of the Poisson kernel. The experimental and the numerical distributions are in excellent agreement with theoretical predictions for all cases.

We investigate the dynamics of an array of chaotic logistic maps coupled with random delay times. We report that for adequate coupling strength the array is able to synchronize, in spite of the random delays. Specifically, we find that the synchronized state is a homogeneous steady state, where the chaotic dynamics of the individual maps is suppressed. This synchronization behavior is largely independent of the connection topology and depends mainly on the average number of links per node. We carry out a statistical linear stability analysis that confirms the numerical results and provides a better understanding of the nontrivial roles of random delayed interactions.

The phase “jumps” for solitons interacting on a vortex filament, observed in experiments, have been unaccounted for for more than 20 years. Using explicit formulas describing the interaction of two solitons on a thin vortex filament in the localized induction approximation, we show that an appropriate choice of the parameters of the solitons leads to large phase shifts. This result does not depend on the axial flow along the filament.

We present a new approach to the Helmholtz spectrum for arbitrarily shaped boundaries and general boundary conditions. We derive the boundary induced change of the density of states in terms of the free Green’s function from which we obtain nonperturbative results for the Casimir interaction between rigid surfaces. As an example, we compute the lateral electrodynamic force between two corrugated surfaces over a wide parameter range. Universal behavior, fixed only by the largest wavelength component of the surface shape, is identified at large surface separations, complementing known short distance expansions which we also reproduce with high precision.

We consider a nonlinear optical system in general, and a broad aperture laser, in particular, in a resonator where the diffraction coefficients are of opposite signs along two transverse directions. The system is described by the hyperbolic Maxwell-Bloch equations, where the spatial coupling is provided by the D’Alambert operator rather than by the Laplace operator. We show that this system supports hyperbolic transverse patterns residing on hyperbolas in far-field domain, and consisting of stretched vortices in near-field domain.

It is shown that the Husimi representations of chaotic eigenstates are strongly correlated along classical trajectories. These correlations extend across the whole system size and, unlike the corresponding eigenfunction correlations in configuration space, they persist in the semiclassical limit. A quantitative theory is developed on the basis of Gaussian wave packet dynamics and random-matrix arguments. The role of symmetries is discussed for the example of time-reversal invariance.

We study the transition to spatiotemporal chaos in a two-dimensional hydrodynamic experiment where liquid columns take place in the gravity induced instability of a liquid film. The film is formed below a plane grid which is used as a porous media and is continuously supplied with a controlled flow rate. This system can be either ordered (on a hexagonal structure) or disordered depending on the flow rate. We observe, for the first time in an initially structured state, a subcritical transition to spatiotemporal disorder which arises through spatiotemporal intermittency. Statistics of numbers, creations, and fusions of columns are investigated. We exhibit a critical behavior close to the directed percolation one.

We report experiments on mixing of a passively advected fluorescent dye in a low Reynolds number flow in a microscopic channel. The channel is a chain of repeating segments with a custom designed profile that generates a steady three-dimensional flow with stretching and folding, and chaotic mixing. A few statistical characteristics of mixing in the flow are studied and are all found to agree with theoretical and experimental results for the flows in the Batchelor regime of mixing that are chaotic in time. The proposed microchannel provides fast and efficient mixing and is simple to fabricate.

The leapfrogging motion of vortex rings is a three-dimensional version of the motion that in two dimensions leads to exotic exchange statistics. The statistical phase factor can be computed using the hydrodynamical Euler equation, which suggests that three-dimensional exotic exchange statistics is a common property of vortex rings in a variety of quantum liquids and gases. Potential applications range from helium superfluids to Bose-Einstein condensed alkali gases, metallic hydrogen in its liquid phases, and maybe even nuclear matter in extreme conditions.

We show that, by controlling the alignment of molecules, we can influence the high harmonic generation process. We observed strong intensity modulation and spectral shaping of high harmonics produced with a rotational wave packet in a low-density gas of ${\mathrm{N}}_2$ or ${\mathrm{O}}_2$. In ${\mathrm{N}}_2$, where the highest occupied molecular orbital (HOMO) has ${\sigma }_g$ symmetry, the maximum signal occurs when the molecules are aligned along the laser polarization while the minimum occurs when it is perpendicular. In ${\mathrm{O}}_2$, where the HOMO has ${\pi }_g$ symmetry, the harmonics are enhanced when the molecules are aligned around 45° to the laser polarization. The symmetry of the molecular orbital can be read by harmonics. Molecular wave packets offer a means of shaping attosecond pulses.

The eigenfield distribution and the band structure of a photonic crystal waveguide have been measured with a phase-sensitive near-field scanning optical microscope. Bloch modes, which consist of more than one spatial frequency, are visualized in the waveguide. In the band structure, multiple Brillouin zones due to zone folding are observed, in which positive and negative dispersion is seen. The negative slopes are shown to correspond to a negative phase velocity but a positive group velocity. The lateral mode profile for modes separated by one reciprocal lattice vector is found to be different.

A heavy sphere is free to move inside a rotating horizontal cylinder filled with viscous liquid. The steady motion is essentially Stokesian, and the sphere rotates at a fixed location with a lubrication layer between the ball and the wall. The symmetry of the flow field suggests there will be no force to balance the normal component of the ball’s weight. However, we show that a normal force can arise when a cavitation bubble is present. The bubble size was measured as a function of the cylinder rotation rate and agrees well with a model which uses the force and torque balances on the sphere.

We investigate high harmonics generated from rubidium atoms irradiated simultaneously by an intense $3.5\mu \mathrm{m}$ fundamental field and a weak cw diode laser. When $5p$, $5d$, and $4d$ excited states are populated through cascade excitation or deexcitation, orders-of-magnitude increases in harmonic yield as compared with the ground state are observed. It appears that, quite unexpectedly, the population accumulated in the $4d$ state alone is responsible for the observed enhancement.

We report the direct, room-temperature, near-field mapping and spectroscopy of the optical modes of a photonic-crystal microcavity containing quantum wells. We use a near-field optical probe to reveal the imprint of the cavity mode structure on the quantum-well emission. Furthermore, near-field spectroscopy allows us to demonstrate the strong spatial and spectral dependence of the coupling between the sources and the microcavity. This knowledge will be essential in devising future nanophotonic devices.

Landau-Zener tunneling is discussed in connection with optical waveguide arrays. Light injected in a specific band of the Bloch spectrum in the propagation constant can be transmitted to another band, changing its physical properties. This can be achieved using two coupled waveguide arrays with different refractive indices. The step in the refractive index causes wave “acceleration” and thus induces strongly nonadiabatic Landau-Zener tunneling. Theoretically, the analysis is performed by considering a Schrödinger equation in a periodic potential with a step. The region of physical parameters where this phenomenon can occur is analytically determined and a realistic experimental setup is suggested. Its application could allow the realization of light filters.