Photonic crystals of diamond spheres with the opal structure

Opal samples consisting of diamond spheres have been synthesized by chemical deposition in microwave plasma from a CH₄/H₂ mixture using templates of silicon inverse opal. The optical investigations have confirmed that the periodic structures prepared are structurally perfect three-dimensional photonic crystals.     

Hybrid opto-TV image-processing system

Quantum Radiophysics Division. Translated from preprint No. 23, 1991 of the Lebedev Physics Institute, Russian Academy of Sciences, Moscow, Russia.     

SPM bipolar pulsed nanostructuring of graphitic layers

Local ablation of graphitic layers by SPM probe was investigated. The gap between the tip and sample surface was varied. Mono and bipolar electric impulses were applied. Influence of various processing parameters on graphite ablation rates was investigated. Shallow craters and structures with halfwidth as low as 15 nm were produced. Electromechanical mechanism of graphite nanoablation is discussed.     

Phase diagram of the liquid crystal system of water-decanol-lanthanum nitrate-decaethylene glycol monododecyl ether

The phase behavior of a self-organizing system based on the nonionic surfactant of decaethylene glycol monodecyl ether-lanthanum nitrate hexahydrate-water and decanol is presented. A system phase diagram was constructed. The concentration, temperature ranges of existence and types of liquid crystal phases were established. Analysis of structural changes during the phase transitions hexagonal phase-lamellar phase-isotropic liquid was made on the basis of data obtained by viscosimetry and self-diffusion NMR.     

Study of the compounds formed on damaged ZnSe windows by multi-pulse microsecond pulsed TEA-CO2 laser irradiation in air

We report on experimental data of chemical compounds formed in the damaged area at the surface of certain optical ZnSe windows subjected to multi-pulse microsecond pulsed TEA-CO₂ laser irradiation in air. The results are analysed from the viewpoint of implication of the oxidation process activated under the action of CO₂-laser power in plasma initiation and evolution of surface damage process.     

The thermal ionization phase during the plasma formation in TM-1-MH tokamak

The start-up phase of discharge in a TM-1-MH tokamak has been investigated. We present a simple model describing the time evolution of electron density in a time interval where the bulk of electron distribution function is already Maxwellian and thermal ionization of neutral gas dominates. Comparison of the computed results with experimental data proved the validity of this model and allowed us to determine the electron temperature during this period of the discharge. The role of the run-away electron production during the start-up phase is discussed.     

Percolation model of an insulator-conductor transition in ultrananocrystalline diamond films

A percolation model has been proposed to explain an insulator-conductor transition in ultrananocrystalline diamond films upon addition of nitrogen to a gas mixture used to synthesize films. An observed jump of the conductivity by 10–12 orders of magnitude is a result of the rearrangement of the structure of films leading to the formation of diamond nanorods in a graphite shell. A nitriding-induced increase in the volume fraction of these nanorods (up to 0.22) has been determined from small-angle X-ray scattering data. Conduction occurs through graphite shells and the percolation threshold corresponds to the volume fraction of conducting nanorods of 0.06.     

Effect of low-threshold air breakdown on material ablation by short laser pulses

Ablative formation of channels in steel by picosecond and nanosecond pulses of Nd lasers was studied. It was found that significant screening of the incident energy (up to 80–90%) in this pulse duration range is caused by breakdown of air contaminated with ablated microparticles. The breakdown threshold, size of particles, and time of their settling down were estimated. It was shown that this kind of plasma screening results in a decrease in the ablation rate and significant channel widening. Practical approaches to eliminate the low-threshold breakdown induced by microparticles were proposed and implemented. These approaches are based on experimental results of the study of the dependences of laser ablation on the pressure and repetition rate. It was shown that a moderate decrease in the pressure below 300–400 mbar makes it possible to avoid screening. In high-repetition-rate ablation, it was found that values above several kilohertz correspond to quasi-vacuum conditions in the ablation spot.     

Effect of laser radiation parameters on the conductivity of structures produced on the polycrystalline diamond surface

Graphitized structures are fabricated on the polycrystalline diamond surface using an excimer KrF (λ = 248 nm, τ = 20 ns) and a Ti:Al₂O₃ (λ = 400 nm, τ = 120 fs) lasers. It is shown that the conductivity of formed structures is independent of the energy density and the number of pulses per surface point in the case of the excimer laser, whereas such a dependence was observed for femtosecond pulses. The causes of the dependence of the conductivity of surface structures on laser irradiation parameters are discussed.