Amplification of the generation of the sum-frequency signal in multilayer periodic structures at the edges of the Bragg band gap

A new property of a one-dimensional periodic structure — amplification of the sum-frequency signal arising under the simultaneous action of two laser pulses on this structure with radiation frequencies corresponding to the edges of the fixed Bragg band gap — is experimentally observed and described. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 718–721 (10 December 1999)     

Modification of porous silicon in ultrahigh vacuum and contribution of graphite nanocrystallites to photoluminescence

A replacement of the adsorbate in porous silicon is carried out in ultra-high vacuum. The photoluminescence line is shifted and quenched as the products of anodization of silicon — silicon hydrides and atomic and molecular hydrogen — undergo thermal decomposition and desorption. Adsorption of molecular chlorine restores the 560 nm photoluminescence band, which we identified as radiation from graphite nanoparticles. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 106–111 (25 January 1996)     

Fabry-Perot cavity in the field of a gravitational wave

The structure of the electromagnetic field inside a laser cavity—a gravitational-wave detector—is studied. The properties of the spatial and temporal phases of the standing electromagnetic wave are discussed in detail and the corrections appearing in the electric field of the wave as a result of the action of gravitational radiation on the optical system are determined. Zh. éksp. Teor. Fiz. 113, 398–408 (February 1998)     

Glow-discharge-pumped broadband ultraviolet lamp

The optical characteristics of a UV broadband lamp that was excited by a longitudinal glow discharge and operated on Kr—Br₂—I₂, Xe—Br₂—I₂, and Kr—Xe—Br₂—I₂ mixtures are investigated. The interelectrode spacing in the lamp is 10 cm, the inner diameter of a discharge tube being 14 mm. The current-voltage characteristics, the emission spectra of the plasma, and the dependence of the intensity of spectral lines (the amplitude of radiation bands) on the power that was pumped into the plasma based on mixtures of various compositions and pressures, as well as the radiation power in the spectral range from 200 to 390 nm, are studied. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 840–842, November–December, 2005.     

The wideband attenuation of short radio waves on mid-latitude paths during X-ray flares in January 2005

We present the results of the ionosphere oblique chirp sounding on the Cyprus—Nizhny Novgorod, Cyprus—Rostov-on-Don, and Moscow—Rostov-on-Don mid-latitude paths during X-ray flares in January 17, 19, and 20, 2005. It is found that during strong flares the blackout of short radio waves was observed over the entire frequency range of chirp sounding on the Cyprus—Nizhny Novgorod and Cyprus—Rostov-on-Don paths. Modeling of the electron-density profiles in the lower ionosphere based on absorption of short radio waves on the Moscow—Rostov-on-Don path at different stages of the decay of the X-ray radiation intensity is carried out. It is shown that at the instant corresponding to the maximum value of the flare radiation flux, the electron density in the lower ionosphere at altitudes 60–80 km increased by a factor of about 10 and 100 for flares with radiation flux densities 5·10⁻² and 3·10⁻¹ erg/(cm ²·s) in the wavelength range 0.5–4.0 Å which took place in January 19 and 20, respectively. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 1, pp. 1–8, January 2007.     

Parameters of the discharge plasmas of surface-plasma sources of negative hydrogen ions

The main parameters of the plasma of high-current hydrogen-cesium glow discharges of surface-plasma (planotron and Penning) sources of negative hydrogen ions are determined using contact-free spectroscopic methods and compared for identical discharge current densities. The elemental and charge composition of the plasma is established. The temperature of the hydrogen atoms and the energy of the visible-range radiation of the plasma discharge are measured and estimates of the electron density in the plasma are made. The dynamics of the change in the parameters of the discharge plasma of a Penning source — the densities of hydrogen atoms, cesium atoms and ions, and molybdenum atoms — is tracked during a discharge pulse with spatial resolution along two coordinates. It is observed that cesium atoms and ions and molybdenum atoms are pent up near the cathode surface. Zh. Tekh. Fiz. 68, 32–38 (October 1998)     

Kinetics of dislocation ensembles in deformable irradiated materials

The development of plastic instability in the initial deformation stages of irradiated materials is studied. The dependence of the fraction of dislocations which overcome obstacles in the dynamic regime (dislocation “channeling”) on the degree of radiation hardening (irradiation dose) and the dislocation velocity is analyzed. It is shown that this effect plays a role in radiation embrittlement of reactor materials. Fiz. Tverd. Tela (St. Petersburg) 40, 1631–1634 (September 1998)     

Radiation-stimulated diffusion in solids

Irradiation of solids produces a microscopic nonequilibrium state in which the vibrational energy distribution function of the atoms deviates from the thermodynamically equilibrium function. Expressions are obtained for the nonequilibrium distribution function and for the frequencies of activational transitions of atoms out of a potential well. It is shown that the radiation stimulation of diffusion processes involves a deviation of the temperature dependences of the frequencies of transitions of the atoms out of positions of equilibrium from the Arrhenius law. Under subthreshold irradiation conditions the rate of diffusion processes is higher for atoms whose vibrations thermalize over long times and depends linearly on the irradiation intensity. Under above-threshold irradiation conditions the characteristics of cascade regions in solids — their sizes and the vibrational excitation energy of the atoms — can be determined by comparing the computed and experimental temperature dependences of the diffusion coefficient. Zh. Tekh. Fiz. 68, 67–72 (August 1998)     

Nonelectrical method of pumping solid-state lasers

An alternative, nonelectrical method for obtaining a dense radiating plasma and the possibilities of using this method to pump solid-state lasers are investigated. The plasma was obtained experimentally by heating the working gas in a two-stage ballistic plasmatron. A new device — a vortex chamber — is proposed for transferring energy into the plasmatron-laser system. Zh. Tekh. Fiz. 68, 67–70 (September 1998)     

Influence of the Stark effect on multiphoton ionization of atoms when the dynamic polarizability depends strongly on the laser frequency

The influence of the Stark effect on multiphoton ionization of Ba atoms under conditions when the dynamic polarizability depends strongly on the frequency of the laser radiation is investigated. It is found that for some electric field strengths ε of the laser radiation this effect gives rise to resonance peaks in the Ba⁺ ion yield as a function of the laser radiation frequency at frequencies corresponding to single-photon transitions between the excited states. These frequencies can differ substantially from the frequencies corresponding to the conventional multiphoton excitation of these states from the ground states of the atoms. Peaks in the ion yield as a function of ε behave differently from the conventional Stark effect—their position on the frequency scale does not depend strongly on ε. The conditions under which such an induced resonance structure appears are determined. Zh. éksp. Teor. Fiz. 113, 499–512 (February 1998)     

Structures and thermoelectric convection in cholesteric liquid crystals

The possibilities for excitation of electromagnetic field structures and convection cells, i.e., temperature and velocity structures, in a thermotropic cholesteric liquid crystal in the presence of flow are studied. Estimates are made and possible experiments for observing such structures are discussed. A special thermoelectric effect is investigated as the cause of these excitations — the influence of a heating-induced change in the pitch of the cholesteric helix of the molecules on the permittivity and the electric conductivity of the material. Fiz. Tverd. Tela (St. Petersburg) 41, 165–170 (January 1999)     

Critical experiments in the search for fermion condensation

The specific features of fermion condensation — a phase transition associated with the rearrangement of the one-particle degrees of freedom in strongly correlated Fermi systems — by which this phenomenon can be detected experimentally are discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 828–833 (10 June 1997)     

Structural transformations of the cumulene form of amorphous carbyne at high pressure

Structural transformations of the cumulene form of amorphous carbyne which are induced by heating at high pressure (7.7 GPa) are investigated. These can be described by the sequence amorphous phase — crystal — amorphous phase — disordered graphite. Raman scattering shows that predominately the chain structure of carbyne remains at the first three stages. It was found that the intermediate crystalline phase is an unknown modification of carbon whose structure is identified as cubic (a=3.145 Å). A mechanism of structural transformations in carbyne that involves the formation of new covalent bonds between chains is discussed. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 237–242 (25 August 1997)     

Empirically correct electrodynamics

The electrodynamics that predicts all known relevant observations is based upon the force F=(qq ′R/R³) [1 − 2v·v′/c² + 3(v·R) (v′·R)/c²R² + (a — a′)·R/c²] on charge q at r with the absolute velocity v and acceleration a due to charge q′ at r′ with absolute velocity v′ and acceleration a′, where R=r − r′. This force yields Ampere’s original empirical law for the force between current elements, which predicts the many effects due to Ampere tension between colinear current elements. It yields Faraday induction as well as Müller’s localized unipolar induction. The force on an accelerating charge due to a stationary charge yields Lenz’s law for the induced back emf; and, when applied to gravitation, qq′ being replaced by — Gmm′, it yields the inertial force ma, confirming Mach’s priniciple. For charge velocities approaching the velocity of light c it predicts the results of the Kaufmann-Bucherer experiments and the Bertozzi experiment, assuming neomechanics, or mass change with velocity. It is readily written as a field theory. Introducing time retardation, it yields waves and radiation. It predicts the observed zero self-torque on the Pappas-Vaughan Z-shaped antenna. Energy is conserved. The Weber electrodynamic theory is shown to fail.     

229m Th(3/2+, 3.5 eV) and a check of the exponentiality of the decay law

A new object is proposed for checking the exponentiality of the decay law of an isolated metastable state at long times — the anomalously low-lying level 3/2⁺ (3.5±0.5 eV) in ²²⁹Th. Highly efficient excitation of this level by laser radiation in combination with optimal collection of optical photons emitted in an isomeric transition make it possible to achieve measurement times longer than 50T _1/2. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 521–525 (25 April 1998)     

A discrete nonetheless remarkable brick in de Sitter: The “massless minimally coupled field”

Over the last ten years interest in the physics of de Sitter space—time has been growing very fast. Besides the supposed existence of a “de Sitterian period” in inflation theories, the observational evidence of an acceleration of the universe expansion (interpreted as a positive cosmological constant or a “dark energy” or some form of “quintessence”) has triggered a lot of attention in the physics community. A specific de Sitterian field called “massless minimally coupled field” (mmc) plays a fundamental role in inflation models and in the construction of the de Sitterian gravitational field. A covariant quantization of the mmc field, à la Krein—Gupta—Bleuler was proposed in Class. Quantum. Grav. 17, 1415 (2000). In this talk, we will review this construction and explain the relevance of such a field in the construction of a massless spin-2 field in de Sitter space—time.     

Chaotic Rabi vacuum oscillations in cavity quantum electrodynamics

It is shown in numerical simulations with two-level atoms moving through a single-mode high-Q cavity that spontaneous emission of a new type — chaotic Rabi vacuum oscillations — arises in the strong atom-field coupling regime. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 801–806 (10 June 1997)     

Formation of a bistructure of a solid in a computer experiment

Molecular-dynamics was used to investigate the structural changes occurring in a three-dimensional solid when the solid is transferred from an amorphous into a crystalline state. Crystal cells of a new type — pentadecahedrons with five square lateral faces and ten regular triangular faces at the vertices of a cell — were found for the first time in a computer experiment. It is shown that a bistructure consisting of crystal cells of different types, including cells with five-fold symmetry axes, are stable in the solid. Fiz. Tverd. Tela (St. Petersburg) 40, 1919–1924 (October 1998)     

Synchronously pumped femtosecond optical parametric oscillator based on AgGaSe2 tunable from 2 μm to 8 μm

The operation of a continuous-wave mode-locked silver gallium selenide (AgGaSe₂) optical parametric oscillator (OPO) is reported. The OPO was synchronously excited by 120-fs-long pulses of 1.55-μm radiation at a repetition rate of 82 MHz. The 1.55-μm radiation is generated by a noncritically phasematched cesium-titanyl-arsenate (CTA)-OPO pumped by a mode-locked Ti:sapphire laser. The AgGaSe₂-OPO generates signal and idler radiation in the range from 1.93 μm to 2.49 μm and from 4.1 μm to 7.9 μm, respectively. Up to 67 mW of signal wave output power has been obtained. The experimentally determined pulse duration and chirp parameters are in reasonable agreement with results from a numerical model taking into account group velocity mismatch, group velocity dispersion, self phase modulation, and chirp enhancement. Received: 6 August 1999 / Revised version: 4 October 1999 / Published online: 3 November 1999