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International audience; Based on numerical modeling, we compare laser ablation and spark discharge as promising methods of nanoparticle formation. First, we consider spark discharge between parallel plate metal electrodes. Second, we investigate nanosecond laser ablation of a metal target. For both phenomena copper is chosen to be nanoparticle material and argon at atmospheric pressure is used as an ambient gas. Despite different energy inputs, both differences and similarities are revealed in the corresponding plasma properties. The time-evolution of the critical particle sizes are, however, found to be similar in both cases.

Particles generated by 2.94 μm pulsed IR laser ablation of liquid 3-nitrobenzyl alcohol were irradiated with a 351 nm UV laser 3.5 mm above and parallel to the sample target. The size and concentration of the ablated particles were measured with a light scattering particle sizer. The application of the UV laser resulted in a reduction in the average particle size by one-half and an increase in the total particle concentration by a factor of nine. The optimum delay between the IR and UV lasers was between 16 and 26 μs and was dependent on the fluence of the IR laser: higher fluence led to a more rapid appearance of particulate. The ejection velocity of the particle plume, as determined by the delay time corresponding to the maximum two-laser particle concentration signal, was 130 m/s at 1600 J/m2 IR laser fluence and increased to 220 m/s at 2700 J/m2. The emission of particles extended for several ms. The observations are consistent with a rapid phase change and emission of particulate, followed by an extended emission of particles ablated from the target surface.

A method to monitor laser cleaning is presented in this paper. During laser cleaning of contamination, particles are generated and/or ejected from a substrate based on laser ablation and laser-induced fast thermal expansion of contaminants and/or the substrate. An airborne particle counter is used to detect the particles ejected from the substrate during laser cleaning at the same time as the irradiation of the laser beam. The cleaning threshold, cleaning efficiency, cleanliness of substrate and ablation threshold of substrate can be monitored by particle detection.

The condensation of Si clusters, produced by ns-laser ablation, is completed typically after a few μs at sufficiently low pressure of background gas. The photoluminescence from free gas suspended Si-cluster was experimentally observed after a long delay time of the order of a few hundred μs. We show that this delay time is related to long cooling and crystallization processes necessary to reach the state with pronounced particle photoluminescence.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP/MS) has been successfully deployed by researchers at the Pacific Northwest Laboratory for the analysis of Hanford nuclear waste. This effort required research to determine the relative importance of the numerous parameters involved in LA-ICP/MS. These factors include laser parameters and sample matrix variables. The precision in relative concentrations was determined as a function of laser wavelength. Ablation at 355 or 266 nm gave precision of 5–10%, while the value for 532 nm was 25% and for 1064 nm was 40%. Analysis of the data for relative fractionation between elements showed large differences in the IR for volatile vs. refractory elements. The UV ablation gave results that were much less dependent on matrix effects and showed minimal or no fractionation. Measurements of the particle distribution produced by laser ablation prior to transfer to the ICP/MS were made as a function of laser wavelength and pulse energy. These results show that the laser wavelength and pulse energies that provide the best precision and accuracy for analysis of glass or tank waste simulant materials produce particle size distributions with the majority of ablated material present as particles from 0.1–1.0 μm in diameter. This size range is important for quantitative transport to the ICP/MS and for complete digestion of the particles in the plasma. The particle counts were used to normalize the mass spectra of glasses having widely different opacities and laser ablation efficiencies resulting in quantitative analysis of these samples.

A model of cluster-type laser ablation of materials which as a result of the thermochemical reaction can be decomposed into solid and gaseous products, is developed on the basis of the solution of thermoconductivity and mechanical problems. The ablation threshold, size and velocity of macro-particles escaping from YBaCuO superconductor under the pulsed laser radiation, are calculated.

Time-resolved optical absorption spectroscopy has been used to determine the particle densities of Ca, Ca + , Ca ∗ and relative densities of CaF molecules produced by KrF-laser ablation of CaF 2 in air. The time-resolved spectra show a very strong broadening of the absorption lines at short delay times near the surface. The broadening mechanism has been discussed. The spatial and temporal behaviour of the particles in the ablation plume near the surface was found to be strongly affected by both the air atmosphere and the reaction dynamics in the plasma zone.