Collective quantum features of the relaxation of nonlinear polariton excitations
Collective quantum features of the relaxation of nonlinear polariton excitations
B.A. Grishanin
A closed system of equations of the second - moments approximation for the average values and correlation functions of the atomic operators is obtained neglecting the mutual effect of quantum fluctuations of the populations in different atoms. The nonlinearity in these equations is introduced solely by the populations via the diagonal part of the correlation matrix of the atoms. For the case of a rarefied gas a complete investigation of the dynamics of spontaneous superradiation without a phenomenological simplification of the problem of the geometry of the medium is given, i.e., on the basis of an analysis of the collective matrix of the propagation of the excitation. The complete coherence of the superradiation for small Fresnel numbers is established and the coherence is estimated in the general case; the excitation of a very large number of modes and the presence of stochastic intermode beats due to collective frequency shifts which are different for different modes is explained, the dependence of the intensity on the concentration, which is nonquadratic with deviations from quadratic of <10%, and the delay time of the pulse, are refined.
Show AbstractSome optical phenomena of the twilight atmosphere
Some optical phenomena of the twilight atmosphere
A.Kh. Khrgian and N.A. Petrenko
The illumination produced in the twilight by the scattering of light in an aerosol layer of the stratosphere is calculated. It is shown that, particularly under conditions of a clean troposphere, this scattering may explain certain color phenomena that occur at sunset. Observation of these phenomena gives information on the aerosol layers of the atmosphere.
Show AbstractSpectral characteristics of wave motion in the surface layer of reservoirs
Spectral characteristics of wave motion in the surface layer of reservoirs
V.V. Buklanov and A.A. Pivovarov
The results of synchronous measurements of the raising of the water surface, and of the vertical and horizontal components of the velocity of motion of the water at two levels in a deep reservoir are discussed. The autospectra of the measured quantities, the spectra of the square of the coherence of the raising of the water surface and of the vertical component of the orbital velocity, and the phase spectral relations between the vertical and horizontal components of the velocity of motion of the water are presented.
Show AbstractQuasi-uniform layer in the ocean on the water temperature in the seasonal thermocline
Quasi-uniform layer in the ocean on the water temperature in the seasonal thermocline
A.N. Kabbar and A.A. Pivovarov
An analytical solution of the problem is given and the numerical calculations of the effect of the motion of the upper boundary of the quasiuni form layer on the formation of the temperature profile of the water in the seasonal thermocline for different intensities of the turbulent exchange in it are analyzed. The motion of the boundary and the temperature in it are a pproximated by linear functions of time. It is shown that the hypotheses of "freezing" and "self - similarity" of the seasonal thermocline correspond very closely to reality for small turbulent -exchange intensities.
Show AbstractThe necessary conditions for a regular minimum of the scale factor of comoving space
The necessary conditions for a regular minimum of the scale factor of comoving space
V.G. Agakov
The necessary conditions for a regular minimum of the scale factor of a frame of reference of a comoving barotropic medium, free from energy flows are refined.
Show AbstractAn experimental investigation of the disturbances propagating in front of an intense shock wave in xenon
An experimental investigation of the disturbances propagating in front of an intense shock wave in xenon
A.P. Ryazin and Belkasem Ferkhat (Algeria)
An experimental investigation is made using an interferometric method of the state of xenon in front of a shock wave propagating in a channel of square cross section in the range of Mach numbers M = 10-25 for initial pressures of 10, 25, and 34.5 mm Hg. It is established that the prefrontal zone is disturbed mainly in the region of the walls of the shock tube. The disturbance is in the form of a sudden change in compression.
Show AbstractElectron-phonon interaction in the neighborhood of a Van Hove singularity (II)
Electron-phonon interaction in the neighborhood of a Van Hove singularity (II)
Yu.P. Drozhzhov
The interaction between phonons and electrons close to a Van Hove singular point of the S$_2$ type is considered using methods not based on perturbation theory. It is shown that weak interaction considerably changes the spectrum and density of states in the region of the singularity.
Show AbstractThe shape of the hanle signal in crossed beams
The shape of the hanle signal in crossed beams
A.L. Kotkin, V.V. Maiorshin and R.M. Umarkhodzhaev
The shape of the Hanle signals in crossed beams as a function of the spectral composition and polarization of the interrogation beam is investigated experimentally. The shape of the observed signals can be explained by the presence of nonresonant light in the interrogation beam.
Show AbstractControl of the polarization of the emission of a solid-state Nd:YAG laser
Control of the polarization of the emission of a solid-state Nd:YAG laser
V.N. Parygin, A.I. Portnyagin and S.К. Рак
The possibility of controlling the polarization characteristics of the emission of a YAG laser is investigated. A crystal of LiNbO$_3$ is placed in the resonator and a voltage is applied to it. Experiment shows that the plane of polarization of the radiation can be rotated by changing the electric signal applied to the electrooptical crystal.
Show AbstractEstimate of the conditions for the occurrence and the frequency of current oscillations at a virtual cathode
Estimate of the conditions for the occurrence and the frequency of current oscillations at a virtual cathode
Yu.K. Alekseev and A.I. Kostienko
A modified diode with a constant resistance in the collector circuit is considered. The conditions for oscillations to occur at the virtual cathode are analyzed. An expression is obtained for the oscillation frequency by means of which one can calculate the upper frequency limit for some practical cases. An experiment to observe oscillation at the virtual cathode is described.
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