[en] The experimental equipment in combination with pulsed Nd-YAG lasers was developed and applied to investigate co-deposited layer characterisation and ablation. Heating and ablation regimes were distinguished by ablation threshold fluence that was determined experimentally for graphite samples from TexTor (Germany) and TORE SUPRA (France) tokamaks. With 100 ns pulses, the ablation threshold for graphite substrate (2.5±0.5 J/cm²) was much higher than the one for co-deposited layer (0.4±0.1 J cm^-2). These threshold features are very promising to ensure self-controlled laser cleaning without substrate surface damage. The obtained optimal conditions (laser fluence F=1-2 J/cm², 10-20 kHz repetition rate) were applied for co-deposited layer cleaning. The TexTor 50 μm thickness layer was almost completely removed after a single scanning without any damage of the graphite substrate. Cleaning rate of 0.2 m²/hour was demonstrated experimentally for 20 W mean laser power. A theoretical model of a complex surface heating (graphite or metal with a co-deposited layer) was developed to explain the experimental results and to obtain laser cleaning optimisation. A good agreement of the theoretical data with the experimental results was obtained. The studies on LIBS method for co-deposited layer characterisation have determined the analytical spectral lines for hydrogen, carbon, and other impurities (B, Fe, Si, and Cu) in TexTor graphite tile. The obtained results should be regarded optimistic for co-deposited layers characterisation by LIBS method. The development of certain laser methods and their application for in-situ detritiation and co-deposited layer characterisation are presented and discussed. (authors)

[en] Nuclear dismantling faces the challenge of paint removal on large surfaces of painted walls. The conventional methods for paint stripping on concrete walls are mainly based on mechanical grinder and lead to an important volume of aerosols and wastes. Laser ablation has been evaluated as a promising method for paint removal with a number of advantages. The method reduces considerably the waste volume as the removal of paint is selective. The ablated matter can be collected by aerosol aspiration/filtration. The automation of the process can provide a higher capacity of paint removal. Laser ablation of paint was under our extensive studies. Laser ablation with different nanosecond repetition rate lasers was comparatively studied to understand the ablation mechanisms, and to obtain the highest efficiency of paint removal. The investigations were made with three Q-Switched Nd:YAG lasers (λ = 532 nm and λ = 1.064 μm). The different pulse durations (5 ns and 100 ns) demonstrated the different ablation regimes. Ablation with long pulses (100 ns) provided the best removal efficiency while the short ones (5 ns) decreased the ablation threshold fluence. It was demonstrated that the pulse repetition rate increasing in the 20 Hz - 10 kHz range induced heat accumulation in the paint. It resulted in ablation efficiency increase with a large decrease in the ablation threshold fluence. Laser ablation in the 0 - 10 J / cm² fluence range was investigated. Various paints were under investigation to obtain the maximum efficiency of paint removal for each specific experimental case. The ejected matter recording with a high speed imaging system allows to analyse the laser-matter interaction. (authors)

[en] The accurate quantification of nucleic acids is essential in many fields of modern biology and industry, and in some cases requires the use of fluorescence labeling. Yet, in addition to standardization problems and quantification reproducibility, labeling can modify the physicochemical properties of molecules or affect their stability. To address these limitations, we have developed a novel method to detect and quantify label-free nucleic acids. This method is based on stoichiometric proportioning of phosphorus in the nucleic acid skeleton, using laser-induced breakdown spectroscopy, and a specific statistical analysis, which indicates the error probability for each measurement. The results obtained appear to be quantitative, with a limit of detection of 10⁵ nucleotides/μm² (i.e. 2 x 10¹³ phosphorus atoms/cm²). Initial micro-array analysis has given very encouraging results, which point to new ways of quantifying hybridized nucleic acids. This is essential when comparing molecules of different sequences, which is presently very difficult with fluorescence labeling