Thermal signature of LIPSS formation revealed by infrared diagnostics

Abstract

Formation of Laser Induced Periodic Surface Structures (LIPSS) is a very interesting phenomenon. As the process is now moving towards the industry for the production of functional surfaces, a monitoring technique for online process control is needed. In the present work, the process was investigated for the first time using fast infrared radiometry. An advanced multi-beam laser system with 2601 beams using DOE and 200 W picosecond laser was used. Heat accumulation was measured during the 50 pulses of LIPSS fabrication on steel for fluences from 0.07 to 0.31 J/cm2 and frequency 50 kHz. Interestingly, on the cooling part of the curves, plateaus were observed after each laser pulse, for high pulse energies even double plateaus. The observed shapes of the signal evolution in time represent thermal signature of the LIPSS formation. The results are promising that process control will be feasible by monitoring heat accumulation or plateau length.