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Abstract: The ablation properties of aged triterpenoid dammar and mastic films were investigated using a Krypton Fluoride excimer laser (248nm, 25ns). Ablation rate variations between surface and bulk layers indicated changes of the ablation mechanisms across the depth profiles of the films. In particular, after removal of the uppermost surface varnish layers there was a reduction of the ablation step in the bulk that was in line with a significant reduction of carbon dimer emission beneath the surface layers as detected by laser-induced breakdown spectroscopy. The results are explicable by the generation of condensation, cross-linking and oxidative gradients across the depth profile of triterpenoid varnish films during the aging degradation process, which were recently quantified and established on the molecular level. [Copyright &y& Elsevier]

A new approach for the understanding of the energy relaxation dynamics of excited atoms involving a long-lived molecular precursor is presented here for krypton. Excitation of the gas close to the 5 s[3/2] metastable atomic level ( E − E< kT) is achieved with an intense VUV laser source (I ≈ 10 photon/pulse) realized by resonantly enhanced 4-wave mixing (2ω + ω) in room temperature mercury vapor ( N ≈ 10 at./cm). The decay of the II. continuum luminescence (145 nm) is studied. In the pressure range 200-500 mbar, decay rates depend linearly on pressure but have a negative zero-pressure intersect. We show here that this result can be understood as an effect of the exchange of energy between two different 'reservoirs' of atomic (5 s[3/2]) and molecular (1) nature, and can be an inherent peculiarity of the recombination kinetics of excited atoms with several product channels. The efficiency of the model is checked for the Kr/N system. Rate constants for relaxation processes are determined in pure krypton and in Kr/N mixtures. [ABSTRACT FROM AUTHOR]

Single and double ionization of magnesium and calcium atoms following Nd: YAG laser multiphoton excitation at 1064 and 532 nm have been studied by employing pulses of 35 ps and 200 ps duration at intensities of the order of 10-2×10 W/cm. The dependence of ion formation on the laser intensity has been measured and the slopes of the linear parts of the log-log plots and the ratios of saturation intensities for two pulse durations have been compared with the predictions of the scaling law. No evidence for a pure direct double ionization process has been obtained. [ABSTRACT FROM AUTHOR]

Results are reported of laser-induced clustering in mixtures of thioph vapor with nitrogen. The formation of micron size was observed. (AIP) [ABSTRACT FROM AUTHOR]

Abstract. Laser-induced breakdown spectroscopy (LIBS) was used to control the cleaning process of polluted sandstone and medieval stained glass. A combination of a KrF Excimer and LIBS was used to clean areas of the artwork. The spectroscopic study of the plasma emission was used to determine the elemental composition of the crust and the underlying material. The on-line implementation of the spectroscopic technique LIBS to the cleaning process provides important information about the optimal cleaning parameters of artworks from glass and stone in order to avoid over-cleaning. [ABSTRACT FROM AUTHOR]

A semiclassical model based on an orbital following picture to describe the dissociation dynamics of K[ATOTHER]@B|[/ATOTHER]2 (B 1Πu) is outlined. The results of this simple model are in complete quantitative agreement with an exact quantum calculation by Dubs and Julienne based on a half-collision multichannel quantum defect analysis (accompanying paper). These theoretical works give a complete description of the process and indicate that dissociation occurs adiabatically from the Hund’s case (a) to the Hund’s case (c) basis, followed by a sudden recoupling at long range to the Hund’s case (e) basis. The experimentally observed bound–free excitation spectrum and the polarization of the atomic product fluorescence are in excellent agreement with the result of a full thermally averaged calculation based on this theoretical dynamical model. [ABSTRACT FROM AUTHOR]

We have measured the far wing absorption profiles of the MgH2 collision system leading to both the nonreactive formation of Mg* and into two distinct final rotational states of the reaction product MgH (v‘=0, J‘=6, 23). We have observed qualitatively expected behavior including a pronounced red wing in the reactive absorption profile indicating strong reaction probability on the excited attractive potential surfaces. We have also observed novel aspects of the excited state dynamics including reactive vs nonreactive channel competition effects and a strong far blue wing reactive absorption suggesting significant reaction probability even for trajectories on the repulsive surfaces. We have developed a simple theoretical model to semiquantitatively explain our experimental results. This model uses standard quasistatic theory to estimate the absorption probability as a function of detuning between levels of MgH2 and with assumed nonreactive vs reactive branching ratios, accounts for the subsequent evolution on the excited potential surfaces. This theory correctly predicts the overall shapes of the profiles and in general gives reasonable predictions for the relative magnitudes of the wing intensities. [ABSTRACT FROM AUTHOR]

Presents a correction to a study which examined the reactive collision dynamics by far wing laser scattering.