Picosecond laser-induced formation of spikes in a single crystal superalloy

The characteristics of laser-induced periodic surface structures (LIPSS) were investigated after laser irradiation with different pulse duration under a certain range of laser fluence (0.25 ≤ Φ ≤ 1.91 J/cm2) and pulse number (11 ≤ N ≤ 560). Spikes were generated by picosecond laser irradiation in ambient air, in comparison with only periodic ripple structures introduced by nanosecond and femtosecond laser irradiation. Microstructural investigations indicate that these spikes were initiated by the fragment of periodic ripple ridges or corrugation on the smooth surface with subsequent pulses, and their separation increased with increasing the laser fluence. Surface capillary waves associated with the resolidification process can be employed to explain the formation of spikes by picosecond laser irradiation.