[en] Specific features of interaction of high-intensity (10¹⁵ W cm^–2) femtosecond laser pulses with ablated vapour are experimentally studied under a tandem (double pulse) regime of irradiation with a short (Δt = 1 – 11 ns) delay between the pulses. Using interference and shadow photography at a time scale of below 10 ns, data on dynamics of vapour expansion are obtained and the electron density in vapour is estimated. Reasons for observed strong screening of the radiation of the second pulse in a tandem are discussed. (interaction of laser radiation with matter)

[en] We have studied the effect that the substitution of an organic substance (ethanol) for water adsorbate on a CVD graphene–SiO₂/Si interface has on the laser-induced modification of graphene and graphene structures on the SiO₂ film. Scanning probe microscopy has been used to analyse changes in the electronic properties of graphene structures on a hydrophilic substrate in the presence of ethanol and as a result of a laser-induced spatial redistribution of a water–alcohol adsorbate on the interface. It has been demonstrated experimentally that ethanol substitution for water adsorbate leads to an increase in the surface potential of the graphene, which is equivalent to a reduction in its work function with respect to the original level under normal conditions at a relative humidity of air from 30% to 60%. In the laser irradiation zone, we observe an additional increase in surface potential by 30–50 mV. Thus, ethanol makes it possible to tune the laser-induced electronic properties of graphene on a substrate. In addition, it has been shown that the intercalation of ethanol molecules leads to severe temporal instability of the physical properties of graphene structures produced by local laser irradiation. We have demonstrated the possibility of information ‘rewriting’ by low-intensity laser pulses in microregions with a changed surface potential in the presence of ethanol. (interaction of laser radiation with matter. laser plasma)

No abstract available

[en] Results are presented on a complex study of field electron emission (FEE) and structural correlations for nanocrystalline diamond and nitride films. It was found that all the samples studied showed similar dependences of the Fowler-Nordheim work function and effective emitting area on the threshold emission field. Besides it was generally observed that FEE occurred at nanosized regions on the boundary of high and low conducting areas, and peaks of the emission intensity were associated with a lowered surface electron potential. Based on the experimental data, the following mechanism of low-FEE from the materials studied can be supposed. Electrons are transferred from the conducting channel into a vacuum through the low-dimensional region where the emission probability is high due to the quantum well effect. A physical model of the electron escape from a quantum well was analyzed. As follows from the estimations, the quantum size effect, being combined with a moderate field enhancement (the field enhancement factor β=10-100), allows us to explain the observed variation in the energetic parameters for the samples studied. The function of the insulating grains is mainly to support the conducting channels in the sample body. Also, the grains can fulfill an additional function of the heat sink

[en] We study the possibility of increasing the efficiency and quality of laser ablation microprocessing of diamond by preliminary forming an absorbing layer on its surface. The laser pulses having a duration of 1 ps and 10 ns at a wavelength of 1030 nm irradiate the polycrystalline diamond surface coated by a thin layer of titanium or graphite. We analyse the dynamics of the growth of the crater depth as a function of the number of pulses and the change in optical transmission of the ablated surface. It is found that under irradiation by picosecond pulses the preliminary graphitisation allows one to avoid the laser-induced damage of the internal diamond volume until the appearance of a self-maintained graphitised layer. The absorbing coating (both graphite and titanium) much stronger affects ablation by nanosecond pulses, since it reduces the ablation threshold by more than an order of magnitude and allows full elimination of a laser-induced damage of deep regions of diamond and uncontrolled explosive ablation in the near-surface layer. (paper)

[en] A Raman laser based on a synthetic diamond crystal pumped by nanosecond pulses of a 1030-nm Yb : YAG laser and emitting in the IR region at the first and second Stokes wavelengths of 1194 and 1419 nm, respectively, was developed. The conversion efficiency was 34 % with a slope efficiency of 50 % and an average power of 1.1 W at a wavelength of 1194 nm; the average power at 1419 nm was 0.52 W. Frequency doubling of the first Stokes component in a nonlinear BBO crystal resulted in orange (597.3 nm) radiation with a pulse energy of 0.15 mJ, an average power of 0.22 W, and a maximum efficiency of 20 %. (paper)

No abstract available

[en] The spatial and temporal distribution of the self-generated magnetic fields were measured in a laser spark produced by double pulses in air. When an atmospheric air breakdown is produced by two sequential laser pulses a resonance-like phenomenon occurs which can be used for the study of the dependence of the amplitude of self-generated magnetic field on the time separation. The results are compared with those obtained when plasma in air was ignited on metal and dielectric targets. (D.Gy.)

No abstract available

[en] We have demonstrated the possibility of using low-coherence tandem optical interferometry for monitoring the local laser processing of diamond surfaces. Noncontact measurements of the optical thickness of single-crystal diamond plates were performed directly during the exposure of the surface to repetitive intense laser pulses. We investigated the dynamics of the thinning of a single crystal in two radically different regimes of laser etching: ablation (KrF excimer laser, λ = 248 nm, τ = 20 ns) and nanoablation (Ti : sapphire laser, λ = 266 nm, τ = 100 fs). (laser technologies)