No abstract available

[en] We describe a method of generating very high-frequency coherent radiation using an electron beam source with a maximum beam energy of 1.2 MeV. We show that, though the high frequency cutoff for the radiation generated when the beam impacts a target at normal incidence is reduced by transverse beam size effects, it is nevertheless possible to generate much higher frequencies by a judicious choice of the angles of incidence and observation. 5 refs., 4 figs., 1 tab

[en] Superoscillations are oscillations of a wavefield that are locally higher than the bandlimit of the field. Superoscillations have to date been studied primarily in coherent wavefields; here we look at superoscillations that appear in the phase of the correlation function in partially coherent fields. It is shown that a decrease in spatial coherence can in some cases strengthen the superoscillatory behavior, and in others decrease it. Superoscillations are studied in a number of model partially coherent fields, and the influence of coherence on each model is considered. (paper)

[en] In the work a consistent approach is developed for to description of a scalar wave field generated by a system of point coherently emitting sources. In particular, the problem of the maxima and minima of the intensity of the superposition field under the conditions of Fraunhofer diffraction is discussed. The problem of determining the serial number of the wave field maxima is investigated. Generalization of the classical result related to interference, when an initial phase shift is present at two sources, is carried out

[en] Such well-known techniques as radiation echo, the method of quantum beats, and superradiance are widely used in studying relaxation processes both in gases and in condensed media. These techniques are based on coherent processes. The advent of lasers extended extremely the potentialities of these methods in the optical band. Over the last years new spectroscopic methods were developed in optics on the basis of narrow nonlinear optical resonances. The methods proved to be very useful in examining low-pressure gases as they permitted obtaining Doppler free resonances with a homogeneous width. This increased to a great extent a spectroscopic resolution in the optical band and simultaneously permitted studies into relaxation phenomena. A lot of methods to obtain Doppler free narrow resonances have been developed in optics by now. The following methods are widely used in nonlinear laser spectroscopy: 1) Method of saturated absorption. 2) Two-photon resonances. 3) Saturation resonances of stimulated Raman scattering. 4) Method of separated optical fields. (orig./WL)

No abstract available

[en] Observations of extremely high brightness temperatures in astrophysical objects imply that coherent emission processes must be occurring. An emission process may be coherent due to an inverted energy distribution leading to maser action, or due to bunching of particles in a region less than or of the order of the wavelength of the radiation. This paper investigates gyromagnetic emission by bunches using a single particle approach which includes the effects of differing particle velocities on the radiation

[en] We consider the theoretical prerequisites for and experimental papers on the coherent radiation of electromagnetic waves by moving sources whose speed exceeds the speed of light in empty space. Examples of this kind are provided by a light spot or a charged filament incident on an interface between two media. (reviews of topical problems)

[en] A large refractive index without absorption in a closed three-level ladder system with incoherent pumping in the presence of spontaneously generated coherence (SGC) is investigated. It has been found that a large refractive index without absorption can be obtained by choosing proper system parameters. The maximum value of refractive index at vanishing absorption depends on the strength of the SGC parameter.

[en] Published in summary form only