Repulsive Casimir forces

We discuss repulsive Casimir forces between dielectric materials with nontrivial magnetic susceptibility. It is shown that considerations based on the naive pairwise summation of van der Waals and Casimir-Polder forces may not only give an incorrect estimate of the magnitude of the total Casimir force but even the wrong sign of the force when materials with high dielectric and magnetic responses are involved. Indeed repulsive Casimir forces may be found in a large range of parameters, and we suggest that the effect may be realized in known materials. The phenomenon of repulsive Casimir forces may be of importance both for experimental study and for nanomachinery applications.     

Fermi surface of 3d1 perovskite CaVO3 near the Mott transition

We present a detailed de Haas-van Alphen effect study of the perovskite CaVO3, offering an unprecedented test of electronic structure calculations in a 3d transition metal oxide. Our experimental and calculated Fermi surfaces are in good agreement, but only if we ignore large orthorhombic distortions of the cubic perovskite structure. Subtle discrepancies may shed light on an apparent conflict between the low energy properties of CaVO3, which are those of a simple metal, and high energy probes which reveal strong correlations that place CaVO3 on the verge of a metal-insulator transition.     

Evolution of probability measures associated with quantum systems

We derive the evolution equation for probability distributions and characteristic functions of the quantum tomograms associated with the linear and nonlinear evolutions of quantum states.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 142, No. 2, pp. 365–370, February, 2005.     

Early stages of laser graphitization of diamond

A mechanism for photographitization of a free diamond surface is proposed. The quantum-kinetic rate of this process is determined. The graphitization rate is close to zero if the activation energy of the graphitization process is taken as being equal to the binding energy of a carbon atom with the surface (i.e. equal to the sublimation energy of a carbon atom). On the contrary, if the activation energy is close to the energy of C–C bonds, the graphitization process may occur at a noticeable rate and be observed under ‘relatively smooth’ experimental conditions. The temperature rise leads to a considerable increase in the graphitization rates. Preliminary experimental data on the low-rate laser ablation of diamond are presented to support the proposed model of photographitization. An early stage of laser-induced graphitization in the bulk of diamond is also considered. It is found that the nucleation of a ‘tiny graphite drop’ is possible in the bulk of the diamond inside the focal area of a laser beam; the ‘graphite drop’ growth causing the appearance of mechanical stresses in the surrounding regions. The maximum size of the graphite drop is determined, which, when exceeded, leads to mechanical damage of the sample and to a change in the mechanism of laser graphitization. An evident mechanical criterion for laser-induced damage of diamond is proposed. Received: 2 October 2002 / Accepted: 5 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. E-mail: stvn@stankin.ru     

Nonlinear absorption in dielectric layers containing copper nanoparticles

The nonlinear absorption in copper nanoparticles contained in glass matrices is investigated using the Z-scan technique at the wavelength of a picosecond Nd: YAG laser (λ=1064 nm). The experimental data obtained for copper nanoparticle-containing composites synthesized through ion implantation are analyzed. It is demonstrated for the first time that, upon exposure to laser radiation at frequencies outside the range of surface plasma resonance, the nonlinear absorption in metallic particles can be caused by the two-photon effect. The optical limiting due to two-photon absorption is discussed for composites containing copper particles.     

Stimulated light scattering by a fluid surface in the presence of total fresnel reflection

Stimulated scattering of light by a free fluid surface in the case of total Fresnel reflection was considered. For scattering directions which are close to the direction of specular reflection of the ray, simple analytic expressions are derived for the threshold intensity and the spectrum of the scattered radiation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 2, pp. 233–241, February, 1972.     

Die Elektrolumineszenz von Einkristallen von ZnO

Zusammenfassung Der Wert der Spannung des Feldes, die quadratische Abhängigkeit des Leuchtens vom Strom, die äu\erst gute übereinstimmung der Abhängigkeiten der Ionisationszahl von der Spannung, welche experimentell wie auch von der Theorie der Multiplikation der Elektronen ausgehend gewonnen wurden, entsprechen somit dem Mechanismus der Sto\ionisation in ZnO. Diese Schlu\folgerung bleibt, wie zusätzliche Nachprüfungen ergeben, auch bei der Aufhebung einiger Vereinfachungen, die bei der Berechnung vorgenommen wurden (z. B. bei der Berücksichtigung schwächerer Abhängigkeiten(t), k(E), der Breite der Sperrzone von der Temperatur usw.) unverändert.Da im Falle der Isolation der Kristalle von den Elektroden die Herkunft der Oberflächensperren dieselbe bleibt, können die Ergebnisse dieser Arbeit auch für die Deutung der Eigenschaften des Destriau-Effektes in ZnO verwertet werden. Sie können anscheinend auch auf das Leuchten homogener Kristalle von ZnS mit ungefähr gleicher elektrischer Leitfähigkeit und der Sperre an der Kathode bezogen werden.

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We observed the same effect on ZnO single crystals as Destriau and Losev. We studied light emission and the electric properties of single crystals with a rectifying contact, which was switched on in the non-transmitting direction. It was found that the dependence of the number of ionizations on each electron, which passes through the contact, on the voltage, which was determined by comparing the experimental results with the diffusion theory of rectification, agrees with the dependence calculated by means of the multiplication theory of electrons in semi-conductors. The conclusion was reached that inelastic collisions play a greater role in ZnO as the excitation mechanism. The calculated voltage dependence of electroluminescence is very close to the measured dependence.

     

Measurement of the dielectric constant of a shock tube plasma

Measurements of the electrical characteristics of the plasma in waveguide and coaxial shock tubes over the frequency range 200–7300 MHz are reported.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 27–31, February, 1974.     

Dislocation mobility in silver chloride

Stress relaxation test has been used as an indirect method for determination of the velocity-stress exponent for dislocation motion in AgCl single crystals in the temperature range 77 to 423 K. The stress dependence of the velocity-stress exponent has been estimated. A large effect of quenching on the value of the exponent has been found.We wish to thank Dr. F.Vávra for supplying the specimens.