INDUCED BREAKDOWN SPECTROSCOPY; DENSITY; GAS; TEMPERATURE; HYDROGEN; SPECTRA; LIBS

Laboratory plasmas inherently exhibit temperature and density gradients leading to complex investigations. We show that plasmas generated by laser ablation can constitute a robust exception to this. Supported by emission features not observed with other sources, we achieve plasmas of various compositions which are both uniform and in local thermodynamic equilibrium. These properties characterize an ideal radiation source opening multiple perspectives in plasma spectroscopy. The finding also constitutes a breakthrough in the analytical field as fast analyses of complex materials become possible.

POLISHING-INDUCED CONTAMINATION; INDUCED DAMAGE THRESHOLD; X-RAY REFLECTION; REFRACTIVE-INDEX; ROUGHNESS; OPTICS; GLASS; MITIGATION; CRACKS; ELLIPSOMETRY

We report on investigations of the spatial variations of contamination, roughness, and index of refraction of classically manufactured polished fused silica surfaces. Therefore, laser-induced breakdown spectroscopy was used to probe surface and subsurface impurities via the detection of aluminum. Measurements at different positions on the surface of the cylindrical fused silica windows evidenced an almost contamination-free center region, whereas a relatively large contamination area was found close to the edge. In-depth measurements verify the presence of aluminum atoms in the bulk until a depth of several tens of microns for the edge region. In addition, atomic force microscopic measurements show that the surface roughness is larger in the center region compared to the edge. Further, the index of refraction increases from the center region towards the edge as measured via ellipsometry. The results indicate a nonuniform impact of the grinding, lapping, and polishing tools on the surface. The findings turn out to be of specific interest for different applications, particularly for the realization of large-scale high-performance coatings. (C) 2017 Optical Society of America

laser-induced breakdown spectroscopy; plasma modeling; calibration-free approach; quality control of drugs; multivitamin tablet;RELATIVE OSCILLATOR-STRENGTHS; PRECISION-MEASUREMENT; TRACE-ELEMENTS; TRANSITIONS; ARGON

The feasibility of the compositional analysis of drugs by calibration-free laser-induced breakdown spectroscopy (LIBS) was investigated using multivitamin tablets as a sample material. The plasma was produced by a frequency-quadrupled Nd: YAG laser delivering UV pulses with a duration of 5 ns and an energy of 12 mJ, operated at a repetition rate of 10 Hz. The relative fractions of the elements composing the multivitamin drug were determined by comparing the emission spectrum of the laser-produced plume with the spectral radiance computed for a plasma in a local thermodynamic equilibrium. Fair agreement of the measured fractions with those given by the manufacturer was observed for all elements mentioned in the leaflet of the drug. Additional elements such as Ca, Na, Sr, Al, Li, K, and Si were detected and quantified. The present investigations demonstrate that laser-induced breakdown spectroscopy is a viable technique for the quality control of drugs.

laser-induced; plasma emission; molecular spectra;INDUCED-BREAKDOWN-SPECTROSCOPY; LOCAL THERMAL-EQUILIBRIUM; GAS-PHASE REACTIONS; ELEMENTAL ANALYSIS; ISOTOPIC SPECTROMETRY; SELF-ABSORPTION; INDUCED FLUORESCENCE; TITANIUM MONOXIDE; ABLATION PLUMES; FEMTOSECOND

The aim of this paper is the description of the optical emission spectral features of the plasma produced by laser-matter interaction, from a fundamental point of view. The laser induced plasma emission spectra are discussed in connection with the basic mechanisms that take place in the plasma phase at different time delays from the laser pulse. The laser induced plasma being a dynamic system, the hierarchy of the elementary mechanisms changes continuously because the electron number density and the electron temperature decrease during the expansion. As a consequence of this, over the duration of the plasma's persistence the prevailing emitting species changes from ions to atoms and from atoms to molecules. Both atomic and molecular emission spectroscopy are discussed, to convey a complete description of the temporal evolution of laser induced plasma. Current literature, as well as the traditional plasma theories, are presented and discussed in order to give to the reader a general idea of the potentialities and drawbacks of emission spectroscopy in the study of laser induced plasma and its various applications.