Sensitive analysis of carbon, chromium and silicon in steel using picosecond laser induced low pressure helium plasma

• It is demonstrated in this study that highly sensitive quantitative analysis of C, Si and Cr can be performed by employing ps laser at much lower energy of 15 mJ as compared to the 800 mJ high energy required by using ns laser as respoted previously.
• It is further shown that the use of C I 247.8 nm emission line enables the detection to be carried out with less expensive ordinary Czerny Turner spectrometer and can thus avoid the detection use of C I 193.1 nm emission line for sensitive C analysis which requires the use of more expensive high power laser and more complex vacuum Paschen Runge spectrometer.
• In addition to demonstrating the existence of linear calibration lines for C, Si and Cr spectral lines useful for quantitative analysis, the limits of detection achieved in this experiment are estimated to be around 10 μg/g for C, 15 μg/g for Si and 5 μg/g for Cr, which are well below the associated sensitivity thresholds required for quality specification of HSS steel products.

An experimental study has been performed on the gas pressure and laser energy dependent variations of plasma emission intensities in Ar, He and N2 ambient gases induced by picosecond (ps) Nd-YAG laser irradiation on low alloy steel (JSS) samples. The study is aimed to demonstrate distinct advantage of using low pressure He ambient gas in combination with ps laser for the sensitive ppm level detection of C, Si and Cr emission lines in the UV–VIS spectral region. The much shorter pulses of ps laser are chosen for the effective ablation at much lower energy and for the benefit of reducing the undesirable long heating of the sample surface. It is found that the C I 247.8 nm, Fe I 253.5 nm, and Si I 251.4 nm emission lines induced by the ps laser at 15 mJ are readily detected with He ambient gas of 2.6 kPA, featuring generally sharp spectral signals with very low background. The following experimental results using samples with various concentrations of C, Si and Cr impurities are shown to produce for each of those elements a linear calibration line with extrapolated zero intercept, demonstrating the applicability for their quantitative analyses, with a preliminary estimated detection limits of 20 μg/g, 15 μg/g, and 5 μg/g, for C, Si, and Cr, respectively. The possibility of applying the same setup for concentration depth profiling is also demonstrated.