DUAL-PULSE LIBS; INDUCED PLASMA; ABLATION EFFICIENCY; SENSITIVE ANALYSIS; HELIUM PLASMA; FEMTOSECOND; ENHANCEMENT; NANOSECOND; MICROANALYSIS; DEUTERIUM

A time-resolved spectroscopic study is performed by using 125-500 micro-Joule (mu J) ps laser focused directly without the aid of microscope on a Cu plate sample in a variety of low-pressure ambient gases including air, helium and argon. It is shown that the ultrashort mu J laser-induced low-pressure plasma in Ar ambient gas exhibits the typical characteristics of shock wave plasma responsible for the thermal excitation and sharp emission of the analyte atoms. It is found that the highest signal to background (S/B) ratio of about 100 is achieved in 1.3 kPa argon ambient gas and detected with optical multichannel analyzer (OMA) gate delay of 1 ns and gate width of 50 mu s. The emission spectra obtained from pure Zn sample show the effective suppression of the ionic emission with ablation energy around and below 500 mu J. The experimental setup is successfully applied to Cr analysis with low detection limit in steel. In particular, its application to C analysis in steel is demonstrated to resolve the long standing problem of overlapping contributions from the neutral and ionic Fe emission. It is further found that an element of high excitation energy such as fluorine (F) can be clearly detected from a non metal teflon sample. Further, its application to alluminum sample containing various concentrations of Mg, Ca, Fe, and Si impurity elements clearly displays the existence of linear calibration lines promising for quantitative analyses in certain dynamical ranges. Finally, in view of the tiny crater sizes of less than 10 mu m diameter created by the very low ps laserenergy, this technique is promising for micrometer resolution mapping of elemental distribution on the sample surface and its depth profiling. (C) 2017 The Japan Society of Applied Physics

INDUCED BREAKDOWN SPECTROSCOPY; QUANTITATIVE-ANALYSIS; PULSE; HELIUM; LIBS; CONFIGURATION; MICROANALYSIS; ENHANCEMENT; DEUTERIUM; NM

An experimental study is performed on the time-dependent intensity variations of Zn emission focusing on the triplet (Zn I 481.0 nm) and singlet (Zn I 636.2 nm) emission lines induced under three experimental conditions. A single nanosecond (ns) Nd:YAG laser in standard laser-induced breakdown spectroscopy(LIBS) setup is employed for the investigation of direct shock wave-induced emission characteristics with N-2 ambient gas at 0.4 kPa and the different effects of He ambient gas at 2 kPa. An additional two-laser system consisting of ns and picosecond (ps) lasers in an orthogonal setup is used to study the exclusive role of a He-assisted excitation (HAE) process for the generation of those two Zn emission lines. The results of this study consistently exhibit the dominant triplet emission over the singlet emission marked by initial maximum intensity ratios of 8 and 12 obtained from the experiments using a single-laser setup in N-2 and He ambient gases, respectively, indicating the significant contribution of the HAE mechanism to the enhanced and longer lasting Zn emission in He gas. The experiment using the special two-laser setup further demonstrates the exclusive role of the HAE process in the Zn emission featuring an even markedly higher triplet/singlet intensity ratio of 22. Thus, the results of this study suggest the possibly more general nature of dominant triplet emission phenomena previously found in laser-induced He and Ca emission spectra. (C) 2017 The Japan Society of Applied Physics