Spectral kinetic properties and lasing characteristics of diode-pumped Cr<Superscript>2+</Superscript>:ZnSe single crystals

The temperature and concentration quenching of the luminescence of Cr²⁺ ions in Cr:ZnSe crystals is experimentally investigated and the radiative lifetime of the upper lasing level is determined. The values of the cross sections of absorption from the ground state of Cr²⁺ ions in Cr:ZnSe crystals are refined. It is shown that the absorption from the excited state of Cr²⁺ ions is negligible near 1.5 μm. Lasing in Cr:ZnSe single crystals is implemented with an efficiency of 31% and an output power of 186 mW using laser diode pumping at a wavelength of 1.77 μm.     

Microwave-resonance-induced resistivity: evidence of ultrahot surface-state electrons on liquid 3He

Measurements of the dc resistivity of surface-state electrons on liquid helium exposed to microwave radiation are reported. It is shown that the resonant microwave excitation of surface-state electrons is accompanied by a strong increase in their resistivity, which is opposite to the result expected from the previously used two-level model. We show that even a very small fraction of electrons excited to the first excited state and decaying back due to vapor-atom scattering strongly heat the electron system, causing a population of higher subbands. The calculated resistivity change is in good agreement with the observed data.     

Head-on collision of two coaxial vortex rings in an ideal fluid

The opposing motion of two coaxial vortex rings is classified in relation to the initial parameters.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 60–64, July–August, 1989.The authors are grateful to V. V. Meleshko for discussing their results.     

Pressure distribution on the surface of a spherical segment entering a compressible fluid

The pressure on the progressively expanding wetted surface of a spherical segment entering a compressible fluid has been experimentally determined.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 9–14, March–April, 1986     

Influence of the formation of hot excitons on the quantum efficiency of short-wavelength photoelectric conversion in III–V semiconductors

A new excitonic mechanism for decreasing the quantum efficiency of the photoelectric conversion process in surface-barrier structures is considered. This mechanism involves the formation of hot excitons which have a large ionization energy and are not subject to the influence of the barrier electric field. The spectral dependence of the hot photocarrier losses is derived in an explicit form from experimental data on the basis of a previously proposed model and is analyzed. This dependence has two segments with abrupt increases, which are caused by the formation of excitons in the L and X valleys of the semiconductor. Fiz. Tverd. Tela (St. Petersburg) 40, 944–945 (May 1998)     

On the Friedrichs extension of some block operator matrices

We give a matrix representation for the resolvent of the Friedrichs extension of some semibounded 2×2 operator matrices and study their essential spectrum.     

Simplest classical models of topological transitions

It is shown that the simplest classical models of topological transitions have scalar singularity of curvature with a point carrier that is a source of spacetime incompleteness. It is also shown that, close to topological transition, the condition of energy dominance is violated, while the asymptotic behavior of the curvature tensor (increase in curvature on approaching topological transition) and the energy-momentum tensor (violation of the energy-dominance condition) is a common property of the given models and is determined overall by the type of topological transition.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 42–46, December, 1983.     

A model of photostructural changes in chalcogenide vitreous semiconductors: 1. Theoretical considerations

Light-induced processes in chalcogenide vitreous semiconductors are considered in the framework of a configurational model of two stable states (ground and metastable) of atomic units with optical and thermal transitions between these states. Probabilities of these transitions as functions of photon energy and temperature are calculated. an expression for the metastable state population kinetics is given.