Carbon analysis of steel using compact spectrometer and passively Q-switched laser for laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is carried out with compact 1064 nm laser and spectrometer components which are suitable for handheld applications. Bursts of ∼0.6 mJ, 5 ns laser pulses are generated by a passively Q-switched laser with a 1 kHz triggered pump diode. The miniature spectrometer with a set wavelength range of ∼188-251 nm has an instrumental broadening at the carbon analyte line, C I 193.09 nm, of less than 36 pm. Analytical calibration curves of C, as well as Cr, Ni, and Si are taken with certified reference samples of iron and steel in an argon purged setup. The net duration of the laser bursts is ∼0.7-1.4 s for a measurement, depending on the number of repetitions on the sample surface. The limit of detection (LOD) is determined to a mass fraction of 34 µg/g for C. High-alloy steels 1.4306 (0.01% C) and 1.4541 (0.035% C) are separated clearly by the LIBS measurement of carbon.

Laser-induced ablation of a steel sample in different ambient gases by use of collinear multiple laser pulses

The sensitivity of laser-induced breakdown spectroscopy of solid samples depends on the number of ablated and excited analytes. Laser ablation of solid samples can be enhanced by using collinear multiple laser pulses, for example double or triple pulses, rather than single laser pulses with the same total laser pulse energy. The ablation rates and the plasma conditions are affected by the ambient gas. In this study laser ablation was examined by varying the interpulse separation of the multiple pulses, within double and triple-pulse bursts, and the gas mass density at constant gas pressure. Different ambient gases and gas mixtures consisting of argon, oxygen, and nitrogen were used to study their effect on ablation rates. In a pure argon atmosphere (99.999% v/v Ar) the ablation burst number required to penetrate a steel plate of thickness 100 microm is reduced by a factor of approximately six by use of triple-pulse bursts with a symmetric interpulse separation of 15 micros rather than single pulses with the same total burst energy of 105 mJ. For double and single pulses the factors are 1.6 for Ar and 2.8 for synthetic air. Analyte lines are 4 to 8 times more intense if an argon atmosphere, rather than air, is used.