Direct determination of trace elements in powdered samples by in-cell isotope dilution femtosecond laser ablation ICPMS

A method has been developed for the direct and simultaneous multielement determination of Cu, Zn, Sn, and Pb in soil and sediment samples using femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICPMS) in combination with isotope dilution mass spectrometry (IDMS). The in-cell isotope dilution fs-LA-ICPMS method proposed in this work was based on the quasi-simultaneous ablation of the natural abundance sample and the isotopically enriched solid spike, which was performed using a high repetition rate laser and a fast scanning beam device in a combined manner. Both the sample preparation procedure and the total analysis time have been drastically reduced, in comparison with previous approaches, since a unique multielement isotopically enriched solid spike was employed to analyze different powdered samples. Numerous experimental parameters were carefully selected (e.g., carrier gas flow rate, inlet diameter of the ablation cell, sample translation speed, scanner speed, etc.) in order to ensure the complete mixing between the sample and the solid spike aerosols. The proposed in-cell fs-LA-ICP-IDMS method was tested for the analysis of two soil (CRM 142R, GBW-07405) and two sediment (PACS-2, IAEA-405) reference materials, and the analysis of Cu, Zn, Sn, and Pb yielded good agreement of usually not more than 10% deviation from the certified values and precisions of less than 15% relative standard deviation. Furthermore, the concentrations were in agreement not only with the certified values but also with those obtained by ICP-IDMS after the microwave-assisted digestion of the solid samples, demonstrating therefore that in-cell fs-LA-ICP-IDMS opens the possibility for accurate and precise determinations of trace elements in powdered samples reducing the total sample preparation time to less than 5 min. Additionally, scanning electron microscope measurements showed that the aerosol generated by in-cell fs-LA-ICP-IDMS predominantly consisted of linear agglomerates of small particles (in the order of few tens of nanometers) and a few large spherical particles with diameters below 225 nm

Laser fluence, repetition rate and pulse duration effects on paint ablation.

The efficiency (mm3/(J pulse)) of laser ablation of paint was investigated with nanosecond pulsed Nd:YAG lasers (l = 532 nm) as a function of the following laser beam parameters: pulse repetition rate (1–10,000 Hz), laser fluence (0.1– 5 J/cm2) and pulse duration (5 ns and 100 ns). In our study, the best ablation efficiency (h ffi 0.3 mm3/J) was obtained with the highest repetition rate (10 kHz) at the fluence F = 1.5 J/cm2. This ablation efficiency can be associated with heat accumulation at high repetition rate, which leads to the ablation threshold decrease. Despite the low thermal diffusivity and the low optical absorption of the paint (thermal confinement regime), the ablation threshold fluence was found to depend on the pulse duration. At high laser fluence, the ablation efficiency was lower for 5 ns pulse duration than for the one of 100 ns. This difference in efficiency is probably due to a high absorption of the laser beam by the ejected matter or the plasma at high laser intensity. Accumulation of particles at high repetition rate laser ablation and surface shielding was studied by high speed imaging

Laser ablation of a turbid medium : Modeling and experimental results.

International audienceQ-switched Nd:YAG laser ablation of a turbid medium paint is studied. The optical properties absorption coefficient, scattering coefficient, and its anisotropy of a paint are determined with a multiple scattering model three-flux model, and from measurements of reflection-transmission of light through thin layers. The energy deposition profiles are calculated at wavelengths of 532 nm and 1.064 m. They are different from those described by a Lambert-Beer law. In particular, the energy deposition of the laser beam is not maximum on the surface but at some depth inside the medium. The ablated rate was measured for the two wavelengths and compared with the energy deposition profile predicted by the model. This allows us to understand the evolution of the ablated depth with the wavelength: the more the scattering coefficient is higher, the more the ablated depth and the threshold fluence of ablation decrease

Heating and ablation of tokamak graphite by pulsed nanosecond Nd-YAG lasers

International audienceThe results on laser heating and ablation of graphite tiles of thermonuclear tokamaks are presented. Two pulsed Nd-YAG lasers (20 Hz repetition rate, 5 ns pulse duration and 10 kHz repetition rate, 100 ns pulse duration) were applied for ablation measurements. The ablation thresholds (1.0$\pm$0.5 J/cm$^2$ for 5 ns and 2.5$\pm$0.5 J/cm$^2$ for 100 ns laser pulses) were determined for the Tore Supra tokamak graphite tiles (backside) nonexposed to plasma. The high repetition rate Nd-YAG laser (10 kHz, 100 ns pulse duration) and the developed pyrometer system were applied for graphite heating measurements. Some unexpected features of laser heating of the graphite surface were observed. They were explained by the presence of a thin surface layer with the properties different from those of the bulk graphite. The theoretical models of laser heating and near-threshold ablation of graphite with imperfectly adhered layer were developed to interpret the experimental results

Co-deposited layer characterisation and removal control by opticam emission spectroscopy coupled to nano-second laser ablation

International audienceOptical emission spectroscopy coupled with laser ablation has been used to characterise plasma facing components. First results of feasibility studies have shown that specific lines of metallic impurities can be used to discriminate co-deposited layer from substrate (graphite). Recording these lines shot by shot allows to follow in real-time co-deposited layer removal and to evaluate co-deposited layer thickness. It is also possible to evaluate, with this technique, impurity profiles versus depth. Furthermore, last experiments have permitted to record a Hydrogen line indicating that such a technique could be implemented in-situ, in a tokamak, to localise and quantify tritium retention

In situ Tokamak laser applications for detritiation and deposited layers studies

International audienceTreatments of plasma facing components (PFCs) are major issues for ITER operation. Several goals have to be accomplished during these procedures. Among them control of the tritium inventory is one of the most important in order to fulfil safety requirements. In the following paper, a global solution based on laser techniques is presented. Due to its flexibility, to its capability to reach difficult access structures as voids or castellation and its ability to be embarked on robot, laser offers one of the most suitable solution for detritiation of the PFCs via laser ablation process. High ablation efficiency as well as capability to detritiate deposited carbon layer without any interaction with bulk material will be discussed. Then Laser Induced Breakdown Spectroscopy (LIBS) and a new diagnostic based on the study of the surface temperature response after a repetitive pulsed laser heating will be described. It will be shown that used together, they allow the determination both the concentration of tritium in deposited layer as well as the total quantity of carbon deposited on top of bulk material. These two informations are essential to determine when and how long the detritiation process must take place. Finally, open issues needed to be developed in order to use this global laser system in tokamak will be presented

Active multispectral reflection fingerprinting of persistent chemical agents

Remote detection of toxic chemicals of very low vapour pressure deposited on surfaces in form of liquid films, droplets or powder is a capability that is needed to protect operators and equipment in chemical warfare scenarios and in industrial environments. Infrared spectroscopy is a suitable means to support this requirement. Available instruments based on passive emission spectroscopy have difficulties in discriminating the infrared emission spectrum of the surface background from that of the contamination. Separation of background and contamination is eased by illuminating the surface with a spectrally tuneable light source and by analyzing the reflectivity spectrum. The project AMURFOCAL (Active Multispectral Reflection Fingerprinting of Persistent Chemical Agents) has the research topic of stand-off detection and identification of chemical warfare agents (CWAs) with amplified quantum cascade laser technology in the long-wave infrared spectral range. The project was conducted under the Joint Investment Programme (JIP) on CBRN protection funded through the European Defence Agency (EDA). The AMURFOCAL instrument comprises a spectrally narrow tuneable light source with a broadband infrared detectorand chemometric data analysis software. The light source combines an external cavity quantum cascade laser (EC-QCL) with an optical parametric amplifier (OPA) to boost the peak output power of a short laser pulse tuneable over the infrared fingerprint region. The laser beam is focused onto a target at a distance between 10 and 20 m. A 3D data cube is registered by tuning the wavelength of the laser emission while recording the received signal scattered off the target using a multi-element infrared detector. A particular chemical is identified through the extraction of its characteristics pectral fingerprint out of the measured data. The paper describes the AMURFOCAL instrument, its functional units, and its principles of operation