Numerical simulation of the ablation of thin molybdenum films under laser irradiation

Laser irradiation of a molybdenum film on a quartz substrate is numerically studied. The simulated results prove the experimental effect lying in a threefold decrease in the size of the ablation region in comparison with the focal spot. The numerical experiment proves the hypothesis on the two-stage ablation of metal film with the primary formation of oxide phase. It is demonstrated that oxidation leads to a selective decrease in the thermal resistance of the film along the vertical direction, so that the anisotropic character of the ablation is enhanced.     

Synthesis of nanoporous structures in metallic materials under laser action

We defined conditions of the laser-aided formation of nanoporous structures with nanopores ranging in size from 40 to 50 nm using laser pulses of 10.6 μm wavelength at a pulse-repetition rate of up to (4-5)×10³ Hz for a model metallic material (a two-component alloy “brass of 62%”). It has been established that the exposure to a uniform laser light at depths of up to 25-30 μm results in the formation of nanopores with a relatively uniform distribution across the surface. The resulting pattern contains both solitary pores and ramified porous channels. The nanopores are uniformly distributed within a subgrain, being fairly stable in size and shape. The nanopore size and shape feature larger non-uniformity on the subgrain boundary. The resulting metallic structures show promise for use as catalysts and ultrafiltration membranes.     

Physicochemical features of poly-o-phenylenediamine modification with palladium microparticles

A new method is developed to prepare alladium dispersed in a polymeric matrix. Exposure of poly-o-phenylenediamine films in PdCl₂ solution showed palladium cations strongly linked by the polymeric matrix to enable reduction of the metal accumulated in the polymer bulk. Optical absorption spectra were studied for poly-ophenylenediamine saturated with palladium ions and poly-o-phenylenediamine with palladium electroreduced upon impregnation. Method of X-ray photoelectron spectroscopy confirmed the presence of palladium cations in unreduced poly-o-phenylenediamine film and palladium metal upon reduction in polymeric matrix.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.     

Application of a pseudogeometrical optical approach for calculation of the field formed by a focusator

The present work deals with the application of pseudogeometric optics techniques to calculating a light field generated by a focusator of laser radiation into the rectangular domain. We have derived an analytical expression for the principal term of the asymptotic expansion in the focal plane including the geometric-optics shadow domain.     

Specific features of the laser irradiation of thin molybdenum films

Laser irradiation of thin molybdenum films with a thickness of less than 100 nm is studied. An experimental hypothesis in accordance with which films of refractory metals can be laser-ablated owing to the formation of an intermediate oxide phase is experimentally proven. A threefold decrease in the thickness of the ablation region under the action of scanning laser radiation is interpreted.     

Synthesis of a binary DOE focusing into an arbitrary curve, using the electromagnetic approximation

We discuss methods for the generation of desired phase distributions based on the representation of DOEs as an array of diffraction gratings with different direction of grooves and different periods. The formulated problem is solved with due regard for the vector character of the electromagnetic radiation.     

Insulator—insulator—metal plasmonic waveguide for parasitic scattering suppression in plasmonic optics

We have shown using rigorous electromagnetic simulations that a planar structure consisting of two isotropic dielectric layers can be used to reduce parasitic scattering in plasmonic elements by an order-of-magnitude (to 1–3%). The proposed approach can be used for designing various plasmonic elements such as lenses, Bragg reflectors and plasmonic crystals.     

Focusators for laser-branding

A new method is investigated for synthesis of computer-generated optical elements: focusators that are able to focus the radial-symmetrical laser beam into complex focal contours, in particular into alphanumeric symbols. The method is based on decomposition of the focal contour into segments of straight lines and semi-circles, following corresponding spacing out of the focusator on elementary segments (concentric rings or sectors) and solution of the inverse task of focusing from focusator segments into corresponding elements of the focal contour. The results of numerical computing of the field from synthesized focusators into the letters are presented. The theoretical efficiency of the focusators discussed is no less than 85%. The amplitude masks and the results of operational studies of synthesized focusators are presented.