Mechanisms of ultrashort laser ablation in CrMnFeCoNi high-entropy alloy and stainless steel

• Comprehensive analysis of sub-picosecond laser ablation dynamics in CrMnFeCoNi HEA and AISI 304 stainless steel. • Time-resolved pump–probe microscopy utilized to capture transient reflectance changes and ablation dynamics. • Analysis of Newton ring contrasts in spallation regime and absorption in ablation plume in phase explosion regime. • Transfer-matrix method (TMM) employed to correlate transient dynamics with post-ablation measurements. • AISI 304 shows higher absorption and greater vapor formation, suggesting a more photothermal ablation process. High-entropy alloys represent a promising class of materials with potential applications across engineering fields. This study aims to investigate the ultrashort pulse laser ablation dynamics of the high-entropy alloy CrMnFeCoNi in comparison to the conventional austenitic stainless steel AISI 304, focusing on correlating time-resolved pump–probe and post-ablation measurements. Using the transfer-matrix method with pump–probe microscopy, we quantitatively analyze spallation and phase explosion dynamics, linking transient reflectance changes to material-specific ablation mechanisms. Our findings reveal distinct differences in absorption within the ablation plume, with AISI 304 exhibiting a higher absorption of 0.35 compared to 0.2 for CrMnFeCoNi at three times the ablation threshold fluence. This difference indicates a stronger photothermal contribution in stainless steel, accounting for its lower ablation efficiency. Furthermore, the contrast of Newton rings can be well explained by the spallation depth, derived from post-ablation ablation depth measurements. Additionally, we provide insight into the birth (detachment at 10 ps) and death (dissolution between 3 ns and 5 ns) of the spallation layer, enhancing our understanding of transient ablation dynamics. The comprehensive analysis of the transient ablation dynamics, along previously reported post-ablation metrics, provides valuable insights into the laser processing of high-entropy alloys with stainless steel as reference.