On dispersion relations for optical media with spatial dispersion

An estimate of the ratio of the contributions of relativistic and nonrelativistic factors to the Kramers-Kronig relations for a medium with spatial dispersion is performed in a form taking into account the relativistic requirement of the finiteness of the velocity of propagation of a signal. Even under conditions of comparatively strong spatial dispersion, in the case of Wannier-Mott excitons in typical semiconductors, this ratio proves to be very small—of the order of 10^?4, which justifies the conventional (nonrelativistic) form of the dispersion relations.     

Chromatic dispersion behavior of Si-NC-Er doped optical fiber

The chromatic dispersion for conventional and Er-doped fibers using the refractive index approximation is examined. A first, analytical method for investigation of dispersion in step index triple clad optical fiber is used. To design of zero-dispersion shifted fiber for optical communication purpose manipulation of the refractive index and radius of the core are considered. We show that in presence of the Si-NC-Er ions, zero-dispersion wavelength is displaced and the dispersion quantity is increased. In this work, we try to optimize system parameters to obtain minimum dispersion and dispersion shifted fiber with control of the doping levels of Er ions and Si-NC as well as doping profiles. For especial case, we assumed the Gaussian inhomogeneous core refractive index for zero-dispersion wavelength and dispersion managements.     

Time dispersion effects of optical fibre joints

The time dispersion effects of a joint between two fibres are investigated. A general closed form expression is derived for the r.m.s. pulse width of a pair of different graded-index fibres separated by a joint. Numerical computations are reported for some cases of practical interest.     

Low-frequency optical phonons in silica

Measurements of low_frequency Raman spectra of silica fibers under longitudinal tensions as a function of temperature have been correlated with the measurements of FIR spectra of bulk silica in reflection and transmission. The results indicate existence of an LO-TO pair of a low-frequency optical phonon branch in amorphous silica.     

Ultrashort-laser-pulse absorption with spatial dispersion and nonlocal transport effects

We study ultrashort-laser-pulse absorption and plasma heating at a sharp plasma–vacuum interface using advanced models for all-range plasma permittivity and nonlocal heat transport. The electron response includes both collisional and collisionless dissipative effects in the plasma of an arbitrary ion charge. We show that nonlocal electron heat transport is important for correct determination of the value of electron temperature and spatial temperature profile. Nonlocal electron heat flux comes into play after electrons heat up to temperatures of the order of 1 keV and to temperatures several times less for low-density targets.     

Low-frequency optical conductivity of inhomogeneous alloys

The optical conductivity of PdMn_0.7Fe_0.3, Pd₂AuFe, and GdCu alloys with different degrees of homogeneity has been measured. Possible reasons for a low-frequency (E < 1 eV) anomalous maximum in the σ(ω) curves are discussed. The deviation from the Drude behavior of σ(ω) is assigned to the presence of small “metallic” inclusions in the high-resistivity matrix of these alloys.     

Analytic description of optical bistability including spatial effects

Steady-state features for both absorptive and dispersive bistability are obtained analytically with the inclusion of spatial effects. Both Fabry-Perot and ring-cavity geometries are treated using an analytic integration of coupled field equations for counter-propagating waves in a homogeneously broadened two-level medium. The mean-field limit is rigorously introduced starting from exact solutions. Mean-field state equations for both Fabry-Perot and ring cavities are obtained. In the former case explicit comparisons are made with results arising in the approximate treatment of standing waves.     

High-frequency asymptotic behavior of T-odd optical effects

It is shown that the contribution of low-frequency excitations with characteristic energy ℏω _l to T-odd (nonreciprocal) optical effects, including spatial dispersion effects, at optical frequencies ω≫ω _l can be calculated in the zeroth-order approximation with respect to the parameter ω _l/ω. This greatly simplifies their analysis. Some of these effects are found to be frequency independent in the spectral regions where the refractive index n(ω)≈ const. It is shown that frequency-independent Faraday rotation can be observed in media with zero magnetization, including in media with zero microscopic magnetic moment density. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 7, 510–513 (10 April 1999)     

Low-frequency resonance dispersion of sound in the bubble media

Results of experimental studies of low-frequency acoustics of gas-liquid bubble media aimed at the check-up of the theory of resonance dispersion of sound of a new type are presented. According to the theory, together with well-known high-frequency dispersion of sound in the gas-liquid media, connected with resonance of volumetric bubble oscillations and, respectively, with resonance compressibility, there should be lowfrequency resonance dispersion of sound caused by resonance of related spheroidal-progressive bubble oscillations and, correspondingly, by resonance of the efficient dynamic density of a medium. It is shown that experimental data on the velocity and attenuation coefficient of sound in the bubble media prove the existence of resonance dispersion caused by related progressive-deformation oscillations of bubbles. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 05-02-96720) and Obninsk Administration.     

Nonreciprocal effects in active nonlinear optical fibers with nonlinearity dispersion

The nonreciprocity of the dynamics of Gaussian optical pulses propagating in inhomogeneous nonlinear active optical fibers with nonlinearity dispersion is considered. A substantial nonreciprocity of the time of pulse propagation along the optical fiber in the forward and backward directions is revealed. The possibility of realizing the regime of superluminal propagation of a pulse in one of the directions of the optical fiber is indicated.     

Birefringence effects induced by optical saturation, dispersion effects in the far infra-red.

It has been demonstrated recently, using computer simulation, that a molecular liquid treated with strong electromagnetic radiation becomes birefringent in the far infra red region of the electromagnetic spectrum This appears to be a new observation, opening the way for the spectral investigation of molecular dynamics with powerful laser fields. It is shown in this paper that the birefringence is accompanied by dispersion at frequencies characteristic or the molecular dynamics on the picosecond time scale. Dispersion of the birefringence that accompanies dynamic optical saturation is a new practical method of investigating molecular material at far infra red frequencies.     

Low-frequency complex magnetic susceptibility of magnetic composite microspheres in colloidal dispersion

A procedure is presented to determine the permanent magnetic dipole moment of composite microspheres containing magnetic nanoparticles with a blocked magnetic dipole moment. The composite particles are dispersed in a solvent, and the complex magnetic susceptibility is measured from 0.1 to 1000 Hz using a highly sensitive new setup. Composite particles with a permanent magnetic dipole moment are revealed by a characteristic frequency that corresponds to the Brownian rotation of the microspheres. From measured susceptibility spectra, we calculate the permanent magnetic dipole moment of recently developed cobalt ferrite-doped silica and latex microspheres.     

Inverse dielectric function of a superlattice including local field effects and spatial dispersion

The inverse longitudinal dielectric function of a superlattice is calculated. Local field effects due to the superlattice structure and spatial dispersion due to both the superlattice and atomic structure are taken into account. Two applications are treated i) density Raman scattering from interface and bulk plasmons and ii) optical dielectric constants of superlattices.     

Mie theory with spatial dispersion

The classícal Mie theory for the scattering and absorption of electromagnetic radiation by a sphere is extended to the case of a dieelectric sphere which exhibits spatial dispersion. This is achieved by imposing the usual Maxwell boundary conditions as well as Pekar's additional boundary conditions at the surface of the sphere.     

Saturation behavior of a one-pump fiber optical parametric amplifier in the presence of the fourth-order dispersion coefficient and dispersion fluctuation

The influence of the fourth-order dispersion coefficient on the behavior of parametric gain and saturation power of a one-pump fiber optical parametric amplifier over a signal wavelength span in the presence of fiber random dispersion fluctuations was investigated. The output signal power for the parametric gain calculation was obtained by numerically solving the three-coupled amplitude equations. Based on the calculations of the parametric gain over a variation of the signal wavelength, it is found that the saturation power behavior is dependent on the behavior of parametric gain. The manipulations of signal wavelength and the fourth-order dispersion coefficient changed the phase-matching condition, thereby affecting the resulting parametric gain and saturation power.     

Low-frequency behavior of beads constrained on a lattice

We study sound propagation in a triangular lattice of spherical beads under isotropic stress. Polydispersity of real beads breaks some contacts, creating a disordered lattice of contacting beads. At large stress, the sound velocity behaves according to Hertz contact law and departs from it at lower stress. This evolution is reversible, with the same crossover when increasing or decreasing the stress, for a given piling. Correlations are much more sensitive to disorder. When calculated with signals propagated in the same lattice, they evolve reversibly with the stress, being much higher at large stress when the contact lattice is more regular. This leads to an interpretation of the non-Hertzian behavior in terms of progressive activation of contacts, in discrepancy with previous models involving buckling of force chains.     

On the dielectric properties of molecular crystals: II. First-order spatial dispersion and optical activity

The general formal expression for the wavevector- and frequency-dependent dielectric susceptibility tensor of a simple molecular crystal, derived in paper I, is applied to the case of a Bravais lattice with gyrotropic molecules. The dielectric susceptibility tensor is calculated with first-order spatial dispersion and from this an expression for the gyration tensor is derived. As an example the optical rotary power is calculated for light propagating along the optical axis of a gyrotropic tetragonal crystal.