Deep ablation and LIBS depth elemental profiling by combining nano- and microsecond laser pulses

Abstract A combination of nano- and microsecond pulses has been suggested for LIBS elemental profiling beyond 1 mm depth for metal coatings. Deep laser ablation and LIBS measurements have been compared for different laser pulse temporal shapes: single and double nanosecond pulses, free-run pulse and combined micro-nanosecond pulse. The deepest laser crater was produced by free-run pulse but plasma emissivity fell dramatically within the first few laser shots. Both single nanosecond pulse and double nanosecond pulse ablation provided crater with depth less than 0.6 mm which is not enough for a typical cladded coating thickness measurements. Nano- and microsecond laser pulses coupling resulted in deep crater formation (> 1.5 mm) but LIBS spectra with good signal-to-noise ratio can be still captured. The feasibility of LIBS depth profiling by coupled nano- (first) and microsecond (second) pulses has been demonstrated for 0.8–1.2 mm thick superalloy coatings measurements.