Vol 24, No 1 (2016)

A calculation model has been developed to describe the propagation of magnetostatic waves in a periodic structure consisting of two one-dimensional magnonic crystals, the periods of which are shifted relative to each other in the wave propagation direction. It is shown that, depending on the shift between the magnonic crystals, up to three bandgaps can be formed in this structure in the first Bragg resonance.

Anomalous Bloch oscillations in arrays of coupled waveguides have been investigated using two different approaches: multiple scattering formalism and coupled-mode model. Both approaches are shown to yield identical results. Formulas for the parameters of the coupled-mode model are derived. An analytical expression for the optical beam path is obtained, and the condition for the existence of anomalous Bloch oscillations is found.

Fractal pattern analysis is performed for aperiodicmultilayer systems with metamaterials. Morphological features of pattern formation in optical characteristics of structures with different geometry are revealed having regard to the manifestation of the phase-compensation effect and presence of metamaterial layers.

The behavior of the phases of high-order harmonics generated upon interaction of intense laser radiation with matter is investigated. Some specific features typical of the harmonic phases in the high-frequency part of plateau (cut-off harmonic phases) are found. First, the phase difference between neighboring harmonics is a constant value. The width of the spectral range in which this regularity occurs determines the minimum duration of the attosecond pulse obtained from these harmonics by the so-called amplitude gating technique. Second, it is shown that the phase of each harmonic in the cut-off region depends linearly on the laser intensity. The proportionality coefficient is the same for all harmonics in this region and proportional to the cube of laser wavelength. Thus, this dependence is especially important for generating high-order harmonics by lasers with a wavelength of few micrometers.

Influence of transverse effects on the propagation of light beams in gradient glass fiber and on the pulsed mode of the second harmonic generation is investigated. Within the approaches under consideration the equations for the pulse or beam field envelopes are reduced to a system of hydrodynamictype equations for amplitudes and eikonals. These equations are used to describe the vortex and non-vortex beam channeling modes and the propagation of light bullets.

The Raman scattering signal at the second harmonic (532 nm) of cw Nd:YAG laser in a 0.5-μm-thick methyl hydroxyethyl cellulose film on a gold substrate is found to be attenuated when a platinum-iridium probe (with a tip radius of about 10 nm) of a scanning tunnel microscope is brought close (at a distance of 6 to 8 nm) to the surface. The fluorescence signal barely changes under these conditions.

The temperature transformation of submillimeter dielectric spectra of Rochelle salt is analyzed within the framework of dynamic conductance model. The branched network of hydrogen bonds and crystallization water molecules in Rochelle salt is supposed to form a quasi-localized vibrational mode in the crystal spectrum. This mode determines the resonant dielectric response at helium temperatures, which with an increase in temperature is transformed into the relaxation response of diffusion motion.

Acousto-optic properties of the KDP crystal are analyzed with application to wide-angle acousto-optic tunable filters. The analysis is based on the measurements of the effective photoelastic constant in KDP crystals at the optical wavelengths of 405, 532.5, and 633 nm. The disagreement between the experimental and literature data is discussed.

A program for calculating characteristics of acousto-optic interaction in biaxial crystals is developed and used to analyze light diffraction by ultrasound in an iodic acid crystal. Crystal cuts with maximum acousto-optic figures of merits are found. It is shown that in the region of the optical axes the frequency dependences of the Bragg angles under anisotropic diffraction are substantially different from those in uniaxial crystals.

We present results of modeling and simulation of the harmonic and intermodulation distortions as well as the intensity noise of high-speed semiconductor lasers under two-tone modulation. Multiple quantum-well lasers are considered, which are characterized by large differential gain and a modulation bandwidth of about 25GHz. The study is based on the rate equation model of semiconductor lasers excited by injection current with two sinusoidal tones separated by a radio frequency. The modulated laser signal is modeled in both the time and frequency domains. The time domain characteristics include the fluctuating waveform, while the frequency domain characteristics include the frequency spectrum of the relative intensity noise (RIN), carrier-to-noise ratio, modulation response, harmonic distortion, and the second- and third-order intermodulation distortions (IMD2 and IMD3). The analysis is performed for three frequencies of 5, 15, and 24 GHz, which are, respectively, lower, comparable, and higher than the laser relaxation frequency. The range of the modulation depth covers the regimes of small and large-signal modulation. We show that both RIN and IMD3 of two-modulated laser are minimum when the modulation frequency is 5GHz, and maximum when the modulation frequency is 24 GHz. The second-order harmonic distortion, IMD2, and IMD3 values are larger in the vicinity of relaxation oscillations and increase with the modulation index, especially under large-signal modulation.

The shear wave velocity is measured in calibrated polymeric CIRS phantoms containing various spheres of two diameters located at different depths. The measurements are performed at the Verasonics ultrasound system using the method of the shear wave elasticity imaging.

The results of direction finding of broadband pulses from a pneumatic source, towed along an arc at a distance of 11 to 12 km, using spatial-diversity scalar detectors and vector-scalar modules are compared. The problem of direction finding based on power flux and according to a new method, using artificial vectors constructed from components of only vibration velocity vector, is solved. It is shown that, despite the complicated conditions for sound propagation, the error of direction finding using 100-m-aperture scalar detectors and single (point) vector-scalar detectors is almost the same and does not exceed 1 to 2°. The results of direction finding according to all algorithms are in good agreement. A method for suppressing noise from a local source by a four-component vector-scalar detector has been developed and investigated. A real possibility of increasing the signal-to-noise ratio on scalar detectors to 10−15 dB is established. Application of the developed suppression algorithm is found to increase noise immunity of the detection and direction finding.