THz generation via optical rectification with ultrashort laser pulse focused to a line

We report on efficient THz pulse generation via optical rectification with femtosecond laser pulses focused to a line by a cylindrical lens. This configuration provides phase-matched conditions in the superluminal regime. 35 pJ THz pulses have been generated with this technique in a stoichiometric LiNbO₃ crystal pumped by 2 μJ femtosecond laser pulses at room temperature. An unusual superquadratic rise of the THz pulse energy with the laser pulse energy has been observed at high laser energies. This extraordinary energy dependence of the THz generation efficiency is explained by self-focusing of the laser beam in the crystal. Z-scan measurements and comparison of the THz pulse spectra created with laser pulses having different energies confirm this interpretation.     

Formation of silicon carbide and diamond nanoparticles in the surface layer of a silicon target during short-pulse carbon ion implantation

Synthesis of silicon carbide and diamond nanoparticles is studied during short-pulse implantation of carbon ions and protons into a silicon target. The experiments are carried out using a TEMP source of pulsed powerful ion beams based on a magnetically insulated diode with radial magnetic field B _r . The beam parameters are as follows: the ion energy is 300 keV, the pulse duration is 80 ns, the beam consists of carbon ions and protons, and the ion current density is 30 A/cm². Single-crystal silicon wafers serve as a target. SiC nanoparticles and nanodiamonds form in the surface layer of silicon subjected to more than 100 pulses. The average coherent domain sizes in the SiC particles and nanodiamonds are 12–16 and 8–9 nm, respectively.     

Electrical conductivity and band structure of thin polycrystalline EuS films

A study of the electrical resistance of thin polycrystalline EuS films (0.4–0.8 μm thick) in the temperature range 120–480 K has provided the basis for a model of the band structure of this substance. It has been shown that the main impurity levels in thin polycrystalline EuS films are those related with localized states near the conduction band bottom, as well as the E _i donor levels of Eu ions outside regular lattice sites. The “tail” of the localized states extends in energy up to at least ?0.45 eV.     

Track detectors in radiation monitoring of the sunken submarine “Komsomolets”

Track method (using the CN and CR-39 detectors, spark couner of tracks as well as selective sorbents for plutonium and uranium) is applied in 1994 and 1995 together with many other methods in radioecological monitoring of water in the region of the sunken nuclear submarine (NS) “Komsomolets”. The detection assembles were installed with the help of the submersibles MIR. The results obtained inside the NS and on its surface as well as near and on the remote buoy station do not contradict the data obtained by other methods confirming the absence of the plutonium leakage outside of the submarine.     

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.     

Equivalence of Hardy-type inequalities with general measures on the cones of non-negative respective non-increasing functions

Some Hardy-type integral inequalities in general measure spaces, where the corresponding Hardy operator is replaced by a more general Volterra type integral operator with kernel , are considered. The equivalence of such inequalities on the cones of non-negative respective non-increasing functions are established and applied.

     

Ionization spectrum transformation and compression of powerful femtosecond laser pulses in experiments on the propagation in gas-filled dielectric capillaries

The propagation of an intense (I≤10⁶ W/cm²) femtosecond laser radiation with a duration of ～100 fs through gas-filled dielectric capillaries was studied. The radiation with a power up to 0.2 TW propagates along the paths up to 20 cm with a transmission efficiency of ～45%. The beam transverse structure at the output is close to the capillary fundamental mode under gas-ionization conditions. The transformation of pulse spectrum was studied as a function of input intensity. It is demonstrated experimentally that the pulse is compressed to a duration of ～30 fs due to the compensation of ionization-induced self-phase modulation in a linear dispersive element at the capillary output.     

Long-lived plasmoids produced in humid air as analogues of ball lightning

The results of an experimental study of long-lived plasmoids, analogues of ball lightning, are presented. The study focuses mainly on the establishment of the conditions for the prolonged existence of plasmoids in the atmosphere. Experimental setup is described and the observation data displayed in the form of photographic pictures.