arXiv subjects

K. Staliunas

Publications and source records attributed to K. Staliunas.

31 records · Page 2Linked to original sources

arXiv2012

High-Directional Wave Propagation in Periodic Gain/Loss Modulated Materials

Amplification/attenuation of light waves in artificial materials with a gain/loss modulation on the wavelength scale can be sensitive to the propagation direction. We give a numerical proof of the high anisotropy of the gain/loss in two dimensional periodic structures with square and rhombic lattice symmetry by solving the full set of Maxwell's equations using the finite difference time domain method. Anisotropy of amplification/attenuation leads to the narrowing of the angular spectrum of propagating radiation with wavevectors close to the edges of the first Brillouin Zone. The effect provides a novel and useful method to filter out high spatial harmonics from noisy beams.

physics.comp-ph↗

arXiv2011

Formation of collimated sound beams by three-dimensional sonic crystals

A theoretical and experimental study of the propagation of sound beams in- and behind three-dimensional sonic crystals at frequencies close to the band edges is presented. An efficient collimation of the beam behind the crystal is predicted and experimentally demonstrated. This effect could allow the design of sources of high spatial quality sound beams.

cond-mat.mtrl-sci↗

arXiv2010

Spatial Filtering of Sound Beams by Sonic Crystals

We propose and numerically demonstrate an efficient cleaning of spatial structure (spatial filtering) of sound beams by propagating them through at least twodimensional sonic crystals, i.e. through acoustic structures periodically modulated in longitudinal and in transversal direction with respect to the sound propagation direction. We show the spatial filtering in two configurations: with- and without the angular band-gap. We also show that besides the spatial filtering the beams can be additionally focalized at a particular distance behind the sonic crystal in both configurations.

cond-mat.mtrl-sci↗

arXiv2009

Self collimation of ultrasound in a 3D sonic crystal

We present the experimental demonstration of self-collimation (subdiffractive propagation) of an ultrasonic beam inside a three-dimensional sonic crystal. The crystal is formed by two crossed steel cylinders structures in a woodpile-like geometry disposed in water. Measurements of the 3D field distribution show that a narrow beam which diffractively spreads in the absence of the sonic crystal is strongly collimated in propagation inside the crystal, demonstrating the 3D self-collimation effect.

cond-mat.mtrl-sci↗

arXiv2008

Subdiffraction and spatial filtering due to periodic spatial modulation of the gain/loss profile

We investigate light propagation through materials with periodically modulated gain/loss profile in both transverse and longitudinal directions, i.e. in material with two-dimensional modulation in space. We predict effects of self-collimation (diffraction-free propagation) of the beams, as well as superdiffusion (spatial frequency filtering) of the beams in depending on the geometry of the gain/loss lattice, and justify the predictions by numerical simulations of the paraxial wave propagation equations.

physics.optics↗

arXiv2008

Model of a two--transverse mode laser with injected signal

We derive a simple model for a two transverse mode laser (that considers the TEM00 and TEM10 modes) in which an injected signal with the shape of the TEM10 mode but a frequency close to that of the TEM00 mode is injected.

physics.optics↗

arXiv2006

Bistable phase control via rocking in a nonlinear electronic oscillator

We experimentally demonstrate the effective rocking of a nonlinear electronic circuit operating in a periodic regime. Namely, we show that driving a Chua circuit with a periodic signal, whose phase alternates (also periodically) in time, we lock the oscillation frequency of the circuit to that of the driving signal, and its phase to one of two possible values shifted by pi, and lying between the alternating phases of the input signal. In this way, we show that a rocked nonlinear oscillator displays phase bistability. We interpret the experimental results via a theoretical analysis of rocking on a simple oscillator model, based on a normal form description (complex Landau equation) of the rocked Hopf bifurcation

cond-mat.stat-mech↗

arXiv2005

Nonspreading Light Pulses in Photonic Crystals

We investigate propagation of light pulses in photonic crystals in the vicinity of the zero-diffraction point. We show that Gaussian pulses due to nonzero width of their spectrum spread weakly in space and time during the propagation. We also find the family of nonspreading pulses, propagating invariantly in the vicinity of the zero diffraction point of photonic crystals.

physics.optics↗

arXiv2005

Nondifractive Propagation of Light in Photonic Crystals

We show that diffraction of electromagnetic radiation (in particular of a visible light) can disappear in propagation through materials with periodically in space modulated refraction index, i.e. photonic crystals. In this way the light beams of arbitrary width can propagate without diffractive broadening and, equivalently, arbitrary light patterns can propagate without diffractive smearing.

physics.optics↗

arXiv2005

Hyperbolic Transverse Patterns in Nonlinear Optical Resonators

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 DAlambert 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. These structures are described analytically by normal form analysis, and investigated numerically.

physics.optics↗

arXiv2001

Gross-Pitaevskii Model for Nonzero Temperature Bose-Einstein Condensates

Momentum distributions and temporal power spectra of nonzero temperature Bose-Einstein condensates are calculated using a Gross-Pitaevskii model. The distributions are obtained for micro-canonical ensembles (conservative Gross-Pitaevskii equation) and for grand-canonical ensembles (Gross-Pitaevskii equation with fluctuations and dissipation terms). Use is made of an equivalence between statistics of the solutions of conservative Gross-Pitaevskii and dissipative complex Ginzburg-Landau equations. In all cases the occupation numbers of modes follow a k^(-2) dependence, which corresponds in the long wavelength limit (k->0) to Bose-Einstein distributions. The temporal power spectra are of f^(-a) form, where: a=2-D/2 with D the dimension of space.

cond-mat.stat-mech↗

arXiv2001

Spatial and temporal spectra of noise driven stripe patterns

Spatial and temporal noise power spectra of stripe patterns are investigated, using as a model a Swift-Hohenberg equation with a stochastic term. In particular, the analytical and numerical investigations show: 1) the temporal noise spectra are of 1/f^alpha form, where alpha=1+(3-D)/4 with D the spatial dimension of the system; 2) that the stochastic fluctuations of the stripe position are sub-diffusive.

cond-mat.soft↗

arXiv2000

Spatial Solitons in Resonators

We describe experiments testing the existence and investigating the properties of spatial solitons in nonlinear resonators. We investigate the properties of stationary and moving spatial solitons in lasers with saturable absorber, with a subcritical bifurcation, as well as their manipulation. As opposed, spatial solitons relying on a supercritical bifurcation are shown to exist in degenerate 4-wave mixing (DOPO). With a view to technical applications in parallel information processing or communication, experiments on spatial solitons in large area quantum well semiconductor resonators are conducted.

nlin.PS↗