Sensitive in-situ Cr analysis with high resolution and minimal destructive effect using micro-joule picosecond laser generated plasma emission in open ambient air

A study is performed to demonstrate the feasibility of applying a microjoule picosecond laser for sensitive and high resolution in-situ Cr analysis with minimal destructive effect. It is aimed for application to quality assessment of steel products and proses control in the related industry as well as field inspection and monitoring of products in used. The feasibility and realization of these applications is examined and verified by the successful generation of shock wave plasma responsible for the shock wave induced thermal excitation of the ablated atoms by means of a ps Nd:YAG laser operated in the energy range of 100 μJ-500 μJ and directly focused onto the solid sample in open ambient air without the use of microscope and sample chamber as commonly employed in all existing μLIBS techniques. The time-dependent intensity variation of the generated micro plasma emission is shown to exhibit all the well-known characteristic structural and dynamical features of shock wave plasma emission. This is followed by further experiment for the ascertainment of the most favorable laser energy of 500 μJ and gate delay of 100 ns for its applications to Cr analysis of standard steel, standard Al samples and precious green stone sample. The resulted spectra all feature very sharp emission lines with low background and yielding an estimated detection limit of lower than 1 ppm and an average crater size of around 7 μm. It is therefore, promising for minimally destructive and highly sensitive in-situ Cr analysis.