Point source of resonant radiation in an excited dispersive medium

Neglecting the Doppler effect at r , the decay of a single-photon state constantly generated by a foreign atom in a thermally excited medium of two-level molecules is determined by a sum of two exponentials. The asymptotic behavior is determined by the splitting of the energy spectrum of a single-photon state in excited media. This quantum electrodynamic effect has no classical counterpart.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 5–9, October, 1988.     

Point source radiation through a composite medium

The paper considers the acoustic radiation due to a point source in the close vicinity of a composite medium consisting of different fluid strata in motion. The results are derived in general and agree with those obtained in special cases. The most interesting result of the analysis is the prediction of the existence of an “aerodynamic zone of silence” along the vortex discontinuities of the composite medium. Apart from producing the usual reflexion coefficient valid at an interface separating a fluid at rest from a fluid in motion (which is in agreement with the one obtained by Miles [1] and Ffowcs Williams [2]), the analysis also provides a general expression for the reflexion coefficient.     

On source radiation in an isotropic chiral medium

Radiation of external electric and magnetic sources in an isotropic chiral medium is studied by means of decomposition of the electromagnetic field into wave fields of circular polarization and introduction of the corresponding combined sources. The elementary-source fields are calculated using the Green’s function. The wave-field energy flux is discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 87–90, September, 2006.     

Nonstationary source of resonance radiation at the surface of a stimulated dispersed medium

Upon the sudden connection of a radiation source a reflected wave has two fronts corresponding to scattering by excited and nonexcited atoms of the medium. The former turns out to be leading. It is shaped by collapse of a fur coat of virtual photons, because of the vacuum effect, surrounding the excited atoms.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 33–38, October, 1988.     

Influence of an unbounded elastic plate on the radiation of sound by a point source

A sound source is placed at a finite distance from an unbounded elastic place. The source and the plate are submerged in an unbounded fluid at rest. The source has harmonic time dependence. A linear theory is used to compute how much energy is radiated into the fluid and how much energy travels along the plate from the source to infinity.     

Passage of monochromatic radiation through a resonance radiation absorbing medium

The problem of passage of monochromatic radiation pulses through a one-dimensional medium containing several types of nonuniformly distributed absorption centers with coincident energy levels are considered. The physical picture associated with the effect of a brightening wave arising in an optically dense absorbing medium is analyzed. The investigated relations represent a generalization of Bouguer's law for the case of powerful fluxes of monochromatic radiation with allowance for absorption saturation.     

On the scintillations of radiation from an extended source in a randomly inhomogeneous medium

Using the method of refractive scattering of radio waves (RSRW), we solve the problem of space correlation of scintillations of radiation from an extended source in a randomly inhomogeneous medium. General expressions are obtained for the index and radius of the space correlation of fluctuations of intensity of radiation from a source with finite angular dimensions as it propagates though a multilayered medium with refractive index fluctuations. The RSRW method is similar to the diffraction calculation of space correlation of scintillations of an extended source in a thick layer with inhomogeneities. We note that under certain conditions an increase in the number of inhomogeneous layers on the radio wave propagation path leads to a pronounced decrease in the scintillation index and an increase in the space correlation of fluctuations of intensity of received radiation from an extended source. The results obtained have a simple geometric-optical interpretation. We indicate a specific feature in determining the angular dimensions of extended radio sources using the known method of scintillations. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 5, pp. 586–593, May, 1997.     

Elliptically polarized breather in the nonintegrable problem of laser radiation propagation through an isotropic gyrotropic nonlinear medium

A particular analytical solution to the nonintegrable problem of plane electromagnetic wave propagation through an isotropic gyrotropic nonlinear medium is found in the form of elliptically polarized breather. The intensity ratio for the circularly polarized components of this wave, which remains constant during propagation, can be used to determine the ratio of local and nonlocal nonlinear susceptibilities describing the Kerr nonlinearity and its spatial dispersion.     

Aeroelastic flutter of a disk rotating in an unbounded acoustic medium

The linear aeroelastic stability of an unbaffled flexible disk rotating in an unbounded fluid is investigated by modeling the disk-fluid system as a rotating Kirchhoff plate coupled to the irrotational motions of a compressible inviscid fluid. A perturbed eigenvalue formulation is used to compute systematically the coupled system eigenvalues. Both a semi-analytical and a numerical method are employed to solve the fluid boundary value problem. The semi-analytical approach involves a perturbation series solution of the dual integral equations arising from the fluid boundary value problem. The numerical approach is a boundary element method based on the Hadamard finite part. Unlike previous works, it is found that a disk with zero material damping destabilizes immediately beyond its lowest critical speed. Upon the inclusion of small disk material damping, the flutter speeds become supercritical and increase with decreasing fluid density. The competing effects of radiation damping into the surrounding fluid and disk material damping control the onset of flutter at supercritical speed. The results are expected to be relevant for the design of rotating disk systems in data storage, turbomachinery and manufacturing applications.     

Observation of polarized positrons from an undulator-based source

An experiment (E166) at the Stanford Linear Accelerator Center has demonstrated a scheme in which a multi-GeV electron beam passed through a helical undulator to generate multi-MeV, circularly polarized photons which were then converted in a thin target to produce positrons (and electrons) with longitudinal polarization above 80% at 6 MeV. The results are in agreement with GEANT4 simulations that include the dominant polarization-dependent interactions of electrons, positrons, and photons in matter.     

Dyadic Green‘s function for an unbounded gyroelectric chiral medium in cylindrical coordinates

The dyadic Green‘s function for an unbounded gyroelectric chiral medium is formulated in the Fourier domain in cylindrical coordinates.After a triple Fourier integral of the dyadic Green‘s function has been obtained,the integral is reduced by performing the integration over the transverse Fourier variable.     

Hard undulator radiation in an inverse medium

X-ray radiation from fast electrons in undulators filled with an inverse medium is studied. A formula for the spectral density of the number of photons is derived. The intensity zeroth harmonics, as well as the intensity of radiation in zero undulator field, are described by the Tamm-Frank formula for Cherenkov radiation. It is shown that the spectral density of emitted photons in a wavelength range of λ ? 0.4–2.0 Å in such a medium can be increased by four orders of magnitude as compared to the radiation intensity in a vacuum undulator. The energy of emitted electrons in the former case must be in an interval of 5-2 GeV, while electrons with an energy of 14-6 GeV are required in vacuum undulators.

     

Acquisition and processing of angle-resolved photoelectron spectra excited with focussed polarized resonance radiation

A system for the acquisition of angle-resolved photoelectron spectra is described. The sample gas is excited by VUV resonance radiation, which is polarized to about 95% using a fully rotatable fourfold reflection polarizer. One of the mirrors is toroidally shaped in order to focus the radiation into the sample gas cell. This design gives count rates comparable to those obtained by an unpolarized source, and at a greatly reduced background level. A computer controlled system has been developed to automate the recording procedure. It allows for simultaneous recordings of the spectra at the different angular settings, thus eliminating the effects of intensity drifts. Details of calibration procedures and data processing, including spectrum analysis, are given along with a discussion of the accuracy of the results. To illustrate the performance, measured β-values for the main components of the four outermost photoelectron bands in the Hel excited spectrum of CO₂ are presented.     

Proposal for an efficient source of polarized photoelectrons from semiconductors

It is expected that a cesiated semiconductor such as GaAs excited with circularly polarized photons of energy close to the band gap would be a very bright and intense source of polarized electrons. Under easily attainable experimental conditions it is predicted that one could obtain a current of 10^?3–10^?4 A with an electronic polarization close to 50 per cent.