Tunable high-<Emphasis Type="Italic">Q</Emphasis> surface-acoustic-wave resonator

The feasibility of a tunable two-port surface-acoustic-wave resonator is analyzed theoretically and verified experimentally. The center frequency of the resonator is tuned by varying the equivalent length of its cavity. The variation of the center frequency achieved in the experiment is 25 kHz, with the width of the resonance peak being ≈4 kHz at a level of ?3 dB (the loaded Q factor of the resonator is ≈24600) and a frequency of ≈98 MHz. As a result of this study, a tunable resonator controlled by a static electric field that realizes the parameters predicted theoretically is designed. This resonator may serve as a basis for a stable tunable oscillator with a low phase noise.     

Hypersensitivity to small signals in a stochastic system with multiplicative colored noise

Recently we discovered the phenomenon of hypersensitivity to small time-dependent signals in a simple stochastic system, the Kramers oscillator with multiplicative white noise. In the present work we study, theoretically and experimentally with analog simulations, an influence of noise correlation time on hypersensitivity in a nonlinear oscillator with piecewise-linear current-voltage characteristic and multiplicative colored dichotomous noise. We found that the region of hypersensitive behavior is defined by universal scaling index, whereas the specifics of a particular system reveals itself only in the dependence of the above index on system parameters. The dependence of gain factor on noise correlation time is of bell-shaped (resonant) type. Received 27 April 2000 and Received in final form 2 November 2000     

High-transmission two-crystal acousto-optic monochromator

A two-crystal high-transmission acousto-optic monochromator is developed and studied. The transmittance of the monochromator can substantially be increased and the scheme can be simplified using the reflection from a face of the acousto-optic cell as a separating polarizer. The intervals of parameters of acousto-optic interaction (angles and wavelengths) that correspond to high efficiency of the monochromator are found. Characteristics of two high-transmission monochromators with different parameters of the acousto-optic interaction are determined.     

Origin of Bragg-Coulomb high-Tc superconductivity Green''s function and diagram method for umklapp e-e scattering

The Green's function method and diagram technique for umklapp electron-electron scattering mediated by the screened Coulomb interaction in layered anisotropic conductors are examined. Gor'kov-type equations and their general solution for anomalous and normal temperature Green's functions are derived taking into account umklapp scattering of all orders. Explicit equations for dielectric and superconducting order parameters, including coexistent Bragg and BCS pairing, are found. The possibility of the first-order phase transition to the superconducting state is discussed. The theory elucidates the origin of Bragg-Coulomb high-T_c superconductivity, proposed by the authors.     

Method of holographic imaging of inhomogeneities in the density of a substance of a semitransparent medium using plane-parallel laser radiation

A new method for coherent superbroadband sounding of a semitransparent substance with the aim to construct a three-dimensional image of its inner structure is proposed and justified. The method is based on irradiating the studied medium with a plane ray, spectral analysis by the two-dimensional Fresnel–Fourier transform, interferometric comparison of spatial spectra of scattered and reference signals, and holographic construction of a series of two-dimensional images of the medium followed by tomographic reconstruction of its three-dimensional image. The stochastic image model has been justified in a coherent approach for the first time both in the region of high frequencies and after the transfer of the radiation spectrum to the lowfrequency range of spatial frequencies to the surface of the radiation recorder. The spectral correlation characteristics of the speckle structure of the reconstructed image have been studied. Calculations and investigations of the spread function of the structure implementing the proposed method have been carried out.