Spectral dependences of conical emission in gases: Minimization of scattering for ultra-short pulsed laser ablation

Parameters of conical emission (CE), at focusing of femtosecond and short picosecond pulses in ambient gases, are characterized in a wide range of experimental conditions. Scattered and absorbed energy, the beam profiles and spectra are compared for different duration and wavelengths of laser radiation (harmonics of Ti:Sa and Yb:YAG laser). Shorter wavelengths were found to be most beneficial for elimination of CE. Nearly no scattering of short picosecond pulses was observed at 515 nm in the energy density range up to 300 J/cm². The results are analyzed in terms of the contributing ultra-fast phenomena effecting refraction index of gases (the Kerr effect, different mechanisms of ionization). Advantages of the visible pulses are illustrated in deep drilling experiments.     

Self-diffusion in the isotropic and mesomorphic states of the lanthanide-containing system based on nonionic surfactant according to the NMR data

Molecular self-organization in a system based on lanthanum nitrate and the nonionogenic surfactant, viz., decaethylene glycol monododecyl ether, was studied in an aqueous solution and in the liquid-crystalline state. Molecular motion and phase transitions in the system were characterized by the high-resolution pulsed gradient spin-echo ¹H NMR method. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 488–494, March, 2008.     

New type of regular carbon nanostructures: Nanocones on the surfaces of carbon-silicon (a-C:H) composite films

The results of a study of a new type of regular carbon nanostructures, namely, nanocones on the film surfaces of carbon-silicon composites of the (a-C:H):Si type are given in this paper. Nanocones appear under the action of the electric field of the probe of an air-operated scanning probe microscope (SPM) in the case where the values of the voltage amplitude and the exposure times exceed the threshold ones. The produced nanoobjects preserve their shapes at thermal annealing up to 700°C. It is assumed that the process of nanocone formation is related to the local transformation of the carbon-silicon composite structure from the amorphous to the nanocrystalline state in the electric field of the SPM probe.     

High rate deep channel ablative formation by picosecond-nanosecond combined laser pulses

Temporally profiled pulsed radiation of the Nd:YAG laser was applied to drilling and micromachining of ceramics, steel, and CVD diamond, demonstrating one or two orders of magnitude enhancement of ablation rates compared to conventional pico- and nanosecond-pulsed ablation at the same energy density. The developed laser system delivered combined pulses consisting of a picosecond pulse train followed by a nanosecond pulse train. The combination of picosecond and nanosecond components within one laser shot turned out to be especially beneficial for high-aspect-ratio channel formation. Polarization dependence of the ablated deep crater morphology was observed in AlN samples. Waveguide radiation propagation in self-made deep channels as well as the influence of high-temperature laser-produced plasma on this phenomena are discussed.     

Mechanism of UV laser-induced absorption in fused silica fibers

Abstract

An alteration of absorption spectra of fused silica fibers under delivery of high-power (ultraviolet) UV laser radiation (4th harmonic of the Nd:YAG laser, wavelength 266 nm) was studied in comparison with their photoluminescent properties. Tested fibers were produced by various technologies based on PMCVD methods. The nature of defects responsible for UV absorption in fibers and the mechanisms of their photogeneration are discussed.     

Synthesis of carbon films by magnetron sputtering of a graphite target using hydrogen as plasma-forming gas

During magnetron sputtering of graphite using hydrogen as plasma-forming gas, a material sputtered from the target deposited only on heated substrates. When using currentheated Ni-Fe foils as substrates, carbon deposits of different crystal structures were obtained. The conditions for growing single-crystal graphite layers and single- and multilayer graphenes are found by analyzing deposits by Raman scattering.     

Synthesis of Multilayered Diamond Films in Microwave Plasma with Periodic Nitrogen Injections

Doklady Physics - The use of polycrystalline diamond in optics (transparent windows) and electronics (heat sinks) usually requires polishing of a synthesized wafer. However, mechanical polishing of...