Resolving dynamics of acoustic phonons by surface plasmons

We show that the dynamics of acoustic phonons generated by femtosecond impulsive optical excitation can be clearly resolved by a surface plasmon technique, with enhanced sensitivity orders of magnitude higher than regular optical probe measurements. Our calculations confirm that the enhanced sensitivity is an intrinsic property of the surface plasmon probe. Therefore, the surface plasmon technique is a promising tool to detect small signal changes in optical and mechanical properties on a microscopic scale.     

Super Bloch oscillations in the Peyrard-Bishop-Holstein model

Recently, polarons in the Peyrard-Bishop-Holstein model under DC electric fields were established to perform Bloch oscillations, provided the charge-lattice coupling is not large. In this work, we study this model when the charge is subjected to an applied field with both DC and AC components. Similarly to what happens in the rigid lattice, we find that the carrier undergoes a directed motion or coherent oscillations when the AC field is resonant or detuned with respect to the Bloch frequency, respectively. The electric density current and its Fourier spectrum are also studied to reveal the frequencies involved in the polaron dynamics.     

Plasma oscillations in nanotubes and the Aharonov-Bohm effect for plasmons

We theoretically analyze the collective oscillations of 2D electrons in nanotubes. In the presence of a magnetic field parallel to the tube axis, the plasmon frequencies undergo Aharonov-Bohm oscillations. The effect can manifest itself in infrared absorption and in Raman scattering. We calculate the cross sections for inelastic light scattering by plasmons.     

Infrared absorption by surface phonons and surface plasmons in small crystals

A continuum model is developed which describes the infrared absorption of interacting spheres very much smaller than the wavelength of light. A mode with uniform polarization inside the sphere is assumed responsible for the absorption. The frequency of this mode in a small isolated sphere can be greatly shifted from the bulk value due to the surface polarization charge. If the particles are not isolated, this frequency is also influenced by the dipolar interaction of neighboring particles. We find that it is possible to define an average dielectric function for a layer of small interacting, absorbing spheres which has the Lorentz form for either phonon or plasmon excitations. If both plasmon and phonon excitations are possible in the same particle, the absorption coefficient of the coupled system displays two resonances and an antiresonance.     

Observation of anharmonic Bloch oscillations

We report on the experimental observation of Bloch oscillations of an optical wave packet in a lattice with second-order coupling. To this end, we employ zigzag waveguide arrays, in which the second-order coupling can be precisely tuned.     

Damping of Bloch oscillations in the Hubbard model

Using nonequilibrium dynamical mean-field theory, we study the isolated Hubbard model in a static electric field in the limit of weak interactions. Linear response behavior is established at long times, but only if the interaction exceeds a critical value, below which the system exhibits an ac-type response with Bloch oscillations. The transition from ac to dc response is defined in terms of the universal long-time behavior of the system, which does not depend on the initial condition.     

Bloch oscillations of path-entangled photons

We show that when photons in N-particle path-entangled |N,0)+|0,N) or N00N states undergo Bloch oscillations, they exhibit a periodic transition between spatially bunched and antibunched states. The period of the bunching-antibunching oscillation is N times faster than the period of the oscillation of the photon density, manifesting the unique coherence properties of N00N states. The transition occurs even when the photons are well separated in space.     

Interaction of interface plasmons and longitudinal optical phonons in a multilayer structure

The interaction between two-dimensional interface plasmons and longitudinal optical phonons in multilayer structures is analysed in this communication. The dispersion relations for the mixed modes are obtained for periodic boundary conditions in the direction normal to the layer planes. The energy gap between the two bands of mixed modes can be seen in the density of states ?_k(ω) at fixed k parallel to the layers. ?_k(ω) also exhibits singularities at the band edges characteristics of the one-dimensional periodic array of parallel layers.     

Optical Bloch oscillations in waveguide arrays

We show that optical Bloch oscillations can emerge in waveguide arrays with linearly varying propagation constants. The existence of localized modes (Wannier-Stark states) with equidistant wave-number spacing (Wannier-Stark ladder) that do not undergo diffraction is analytically proved. The evolution of arbitrary initial excitations is described, and potential applications are suggested.     

Bloch oscillations in optical dissipative lattices

We show that Bloch oscillations are possible in dissipative optical waveguide lattices with a linearly varying propagation constant. These oscillations occur in spite of the fact that the Bloch wave packet experiences coupling gain and (or) loss. Experimentally, this process can be observed in different settings, such as in laser arrays and lattices of semiconductor optical amplifiers. In addition, we demonstrate that these systems can suppress instabilities arising from preferential mode noise growth.     

On the existence and detection of Bloch oscillations in superlattices

While many predicted superlattice behaviors depend on the presence of Bloch oscillations, the existence of such oscillations remains problematical. Here, we consider procedures by which their existence within a superlattice could be detected. We first set upper and lower bounds on the necessary fields. We then demonstrate that while a negative differential mobility is expected, no resonant peak occurs in this mobility at the Bloch frequency. However, we provide two ways of directly observing Bloch oscillations. In the first, we note the existence of structures in the dc velocity-field characteristic when an externally applied RF field has a frequency which is harmonically related to the Bloch frequency. The second approach is to measure the velocity fluctuation noise spectra, which should have a peak at the field-tunable Bloch frequency.     

Photonic Bloch oscillations of correlated particles

A photonic realization of Bloch oscillations (BOs) of two correlated electrons that move on a one-dimensional periodic lattice, based on spatial light transport in a square waveguide array with a defect line, is theoretically proposed. The signature of correlated BOs, such as frequency doubling of the oscillation frequency induced by particle interaction, can be simply visualized by monitoring the spatial path followed by an optical beam that excites the array near the defect line.     

Resonant delocalization and Bloch oscillations in modulated lattices

We study the propagation of light in Bloch waveguide arrays exhibiting periodic coupling interactions. Intriguing wave packet revival patterns as well as beating Bloch oscillations are demonstrated. A new resonant delocalization phase transition is also predicted.     

Spectral and temporal Bloch oscillations in optical fibres

We report a detailed analysis of experimental parameters and fundamental mechanisms contributing to the strong nonlinear scattering of femtosecond and short picosecond laser pulses (50–6000 fs) at focusing in ambient air and protecting gases. The experimental conditions under consideration are typical for a variety of applications: micromachining of metals and dielectrics, high power laser exposure of targets. Such scattering, being the most noticeable manifestation of the complex phenomenon of conical emission in the focusing geometry, puts fundamental limitations to the incident power of precision laser targeting, restricting in this way potential productivity of micromachining in this pulse width range. The phenomena analyzed here are: ionization, the optical Kerr effect, the distortion of spectra via self-phase modulation, and the refractive ability of microplasma, namely the scattering. Characteristics of the last were investigated with respect to the incident wavelength and pulse width, for focusing of Gaussian and flat-top beams of different diameters. The obtained extensive data allowed us to trace the clue trends and relationships of this phenomenon and to find several ways to reduce or even eliminate the scattering in a broad range of the incident energies.     

Topological solitons and Bloch oscillations in Bose-Einstein condensate

We studied the evolution of topological solitons in the space of its width d and the conjugated momenta l during Bloch oscillations. The unstable solitons are confined in a well with its boundary as four branches of a hyperbola, the stable solitons sit at the four branches of the hyperbola (d · l = 28) which is in agreement with the generalized Heisenberg uncertainty principal Δd · Δl ? Const. The generation, annihilation, and bifurcation of solitons is going on in the well. In studying the behavior of the nonlinear interaction parameter for the stable solitons, it is found that bright solitons and dark solitons alternatively come into action during the breakdown and revival of Bloch oscillations.     

Bloch oscillations in a homogeneous nucleotide chain

It is shown that, at zero temperature, a hole placed in a homogeneous synthetic nucleotide chain with applied electric field demonstrates Bloch oscillations. The oscillations of the hole placed initially on one of the base pairs arise in response to disruption of the initial charge distribution caused by nucleotide vibrations. The finite temperature fluctuations result in degradation of coherent oscillations. The maximum permissible temperature for DNA “Bloch oscillator” occurrence is estimated.     

Magnetic Bloch oscillations in nanowire superlattice rings

The recent growth of semiconductor nanowire superlattices encourages hope that Bloch-like oscillations in such structures formed into rings may soon be observed in the presence of a time-dependent magnetic flux threading the ring. These magnetic Bloch oscillations are a consequence of Faraday's law; the time-dependent flux produces an electromotive force around the ring, thus leading to the Bloch-like oscillations. In the spectroscopic domain, generalized Wannier-Stark states are found that are manifestations of the emf-induced localization of the states.     

Lattice phonons in the presence of non-linear excitations

We examine the interaction between linear (phonon-like) and non linear (kink, soliton-like) excitations of the classical, discrete, ?⁴ chain in the displacive regime. The discreteness of the lattice manifests itself (a) in the asymptotic phonon phase shift, (b) in partial reflection occurring near the Brillouin zone edge and (c) in the spatial shift suffered by a kink due to its collision with a phonon wavepacket. Our analytical results are confirmed by computer simulations.     

Hybridization of optical phonons with double quantum-wire plasmons including drift instabilities

We examine the collective mode spectrum for a double quantum-wire system embedded in semi-infinite polar medium, taking account of the role of optical phonons in interaction with the double quantum-wire plasmons and bulk/surface plasmons. The collective mode frequencies are exhibited as functions of q_x (wavenumber parallel to the wires) and as functions of z₀ (distance of first wire from the interface). We also find that the region of drift instability of the collective modes is split into two disjoint regions of instability by the optical phonons, with a region of stability between them.