Signal strength in high repetition rate ns LIBS: role of heat accumulation and ablation crater overlap effects for stainless steel

In this paper, we have shown that in the case of ns laser–induced breakdown spectroscopy (LIBS), the signal strength of stainless steel first increases and then decreases with an increase in pulse repetition rate. The latter decrease in signal strength may be attributed to the formation of excessive deep craters on the sample, which has been well studied in the literature. However, the initial increase in signal strength has not been reported previously. We proposed that this increase in the signal may be due to a rise in sample temperature as a result of accumulation of residual heat at high repetition rates. Our hypothesis was observed to be well corroborated by experimental and theoretical results. These findings suggest that the plasma signal intensity may be governed by two competing factors: heat accumulation, which dominates at low repetition rates, and ablation crater overlap, which dominates at high repetition rates. Further, our results also showed that a strong and reproducible spectrum can be achieved only within a specific range of pulse overlap rate on the sample.