Laser-induced breakdown spectrometry has been evaluated at high temperatures for stainless steel samples. A Q-switched Nd:YAG laser operating at 1064 nm was used to create a microplasma on an AISI 304L stainless steel sample placed inside a laboratory oven. The steel sample was 51.5 cm away from the focusing lens. The temperature of the samples ranged from 25 to 1200 ³C. The plasma light was collected by means of a ®ber optic bundle, spectrally resolved and then detected by a CCD camera. The effects of sample temperature in the formation of a laser-induced plasma have been studied in terms of its spectral features as well as the morphology of the ablated craters in air at atmospheric pressure. A noticeable dependence of signal emission intensity on sample temperature has been found. Depth pro®ling of stainless steel samples for several temperature conditions was performed. Results have revealed changes in the super®cial composition at temperatures above 600 ³C due to the formation of a slag layer of variable thickness, mainly composed of chromium, iron and manganese oxides.
Multichannel laser-induced breakdown spectrometry (LIBS) is used to generate selective chemical images for silver, titanium, and carbon from silicon photovoltaic cells. A 2.5 mJ pulsed nitrogen laser and a spectrometer using charge-coupled device detection were employed. LIBS images were acquired sequentially by moving the sample located on a motorized x-y translational stage step by step while storing the multichannel LIBS spectrum for each position of the sample, followed by computer-based reconstruction of two-dimensional selective images from intensity profiles at several wavelengths. Depth distributions of carbon impurities are also reported. Room temperature and atmospheric pressure operation as used here remove the restrictions on sample size exhibited by other surface analysis techniques used for imaging applications. Thus, the sample size in LIBS imaging is in principle unlimited. A LIBS experiment does not require a sample to be conductive. Therefore, virtually all materials can be imaged. Although LIBS is a typical example of destructive analytical technique, multichannel detection as demonstrated here confers the possibility to LIBS of obtaining multielement information from a given surface area. Lateral resolution of 80 μm and depth resolution of better than 13 nm were observed. The ultimate limitation to imaging the first layer of the surface in LIBS is the spectral signal-to-noise ratio as dictated by the ablation threshold of the material.
A remote detection system based on optical emission spectrometry of laser-induced plasmas has been developed to record spectra in the visible region from samples placed at remote distances from the excitation source. Unlike from fiber-optic-based systems, light collection is performed remotely as well. Laboratory-scale experiments have shown the possibility of performing real-time analysis of samples placed remotely. The application in the noninvasive analysis of hot samples (at 1,200 degrees C) has been demonstrated as well, allowing the dynamic monitoring of selective elemental migration.
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