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[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] 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)
[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] 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] We reported a new approach for obtaining proper gain coefficient and dithering amplitude of multi-dithering algorithm in coherent beam combination via threshold-testing technique. Through this approach, two parameters can be set based on obtaining threshold with actual signal intensity varying. To clarify the new method, we demonstrated the coherent beam combination of two channels experimentally, which results coincided well with the simulations. The experimental results indicate that this method is an effective way to improve the performance of coherent beam combination systems.
[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)