Theoretical treatments of ultrashort pulse laser processing of transparent materials: toward understanding the volume nanograting formation and “quill” writing effect

The dynamics of ultrashort-laser-induced generation of free electron plasma inside bulk glass is analyzed. The results of modeling are presented for typical glass modification regimes, obtained on the basis of Maxwell’s equations supplemented with the equations describing electron plasma formation and the laser-induced electric current. The model has been demonstrated to allow revealing important features of laser beam propagation in the regimes of dense electron plasma generation such as strong scattering up to complete displacing of light from the plasma region followed by beam refocusing. The geometry of the laser energy absorption zone is determined, and the glass temperature is mapped which may be foreseen at the end of electron–glass matrix relaxation. This, in turn, allows estimating the laser-induced stress levels and making conclusions on the routes of glass modification. Finally, based on the modeling results, the plausible mechanisms are discussed which may be responsible for the formation of volume nanogratings in a number of transparent solids under the action ultrashort laser pulses and laser direct writing anisotropy observed for laser pulses with a tilted front.     

Calculations of ozone line shifting induced by N2 and O2 pressure

Ozone line shifts by nitrogen and oxygen pressure are computed for the ν₁ + ν₃, 2ν₁ and 2ν₃ bands of the 5 μm spectral region by a semiempirical approach. The calculated values agree with measurements better than 0.001 cm^?1 atm^?1 for 98% of O₃–N₂ lines and 87% of O₃–O₂ lines. In contrast with the water molecule case, the polarization components of the interaction potential are shown to contribute to the line shift more efficiently than the electrostatic interactions. As intermediate results, the mean dipole polarizability and the components of the polarizability tensor for the vibrational states (101), (200), and (002) of ozone molecule are determined by least-squares fitting of theoretical shifts to some experimental values. The temperature exponents for the ν₁ + ν₃ band lines are also estimated.     

Formation kinetics of brittle phase nuclei in hydrogenated metals under loading

It is shown that the formation of the brittle phase in hydrogenated metal under external loading is a first-order phase transition. The basic equation of the evolution of elastic stress in a uniform and isotropic hydrogenated metal during the formation of a brittle hydride phase is derived and its solution is found. Based on this data, the time dependences of all characteristics of the phase transition into a brittle phase are found; namely, the densities of nuclei of the hydride phase, the size distribution, and the formation rates of the hydride phase nuclei are found. The characteristic time of the transition into the brittle phase is found.     

Modelling of a nitrogen x-ray laser pumped by capillary discharge

We performed computer modelling of a fast electrical discharge in a nitrogen-filled alumina capillary in order to discover discharge system parameters that may lead to efficient recombination pumping of soft X-ray laser with active medium created by H-like nitrogen ions. The space-time dependences of pinch plasma quantities were found by means of a one-dimensional MHD code. Time dependences of populations of all ionisation states and populations of selected energy levels of lithium-, helium- and hydrogen-like nitrogen ions were evaluated using the FLY code as a post-processor. The population inversion was found at the quantum transition corresponding to the Balmer α-line of N⁶⁺ ions and the resulting gain factor was evaluated for different capillary radii, initial pressure, electric current peaks and periods. A gain factor of 1 cm⁻¹ spanning the time interval of 1 ns was found for an optimised arrangement with capillary radius 1.5 mm, peak current 50 kA, quarter period 40 ns and filling gas pressure 0.5 kPa. It is pointed out that even higher values of the gain factor may be achieved with thinner capillaries and shorter current pulses, e.g. a gain factor of 6 cm⁻¹ is achieved if the capillary radius is 0.5 mm, peak current 56 kA, quarter period 15 ns, and filling nitrogen pressure 3.9 kPa.     

Voltammetric stripping analysis of metal concentrates with polymers soluble in aqueous solutions

The conditions were worked out for the simultaneous stripping voltammetric determination of components of the ternary Pb(II)-Cu(II)-Cd(II) and binary Ag(I)-Cu(II) systems at a carbon-paste electrode in 2% aqueous solutions of the water soluble polymer polyethyleneimine (PEI) and its thiourea-containing derivative (TU-PEI). Water-soluble polymers are shown to reduce the mutual effects of the components of the binary and ternary system at the electrode surface. The different complex stability of Ag(I), Pb(II) or Cd(II) and Cu(II) with PEI and TU-PEI allows Ag(I), Pb(II) and Cd(II) to be determined in the presence of a large excess of Cu(II). Received: 17 July 1997 / Revised: 1 December 1997 / Accepted: 3 December 1997     

Synthesis,X-ray Structure and Mass Spectrum of Cs-C60(CF3)6

C_s-C₆₀(CF₃)₆ was synthesized by the reaction of S₆-C₆₀(CF₃)₁₂ with C₆₀ at 530 °C. Its molecular structure with skew-pentagonal- pyramidal addition pattern was elucidated by single crystal X-ray diffraction. Theoretical DFT calculations were performed to account for a high degree of fragmentation in negative-ion mass spectra.