Ultrashort Pulse Periodic Structuring of Metallic Surfaces
L.F. Mellor, S.P. Edwardson, W. Perrie, G. Dearden and K.G. Watkins
A detailed study has been conducted into the effect of laser process parameters on the production of laser induced periodic surface structures in 316L stainless steel using a pulsed picosecond fibre laser. Periodic structures were produced via scanning of the incident beam at varying speeds in order to control the pulse overlap. Feature depth and uniformity were found to rely heavily upon both the scan speed and pulse energy. Inhomogeneous feature production across the track cross-section was observed and attributed to the Gaussian nature of the incident beam. Features were observed oriented perpendicularly to the direction of polarization for linearly polarized light with a period approximately equal to the incident light wavelength. This period was observed to alter with incident angle and a dependency on laser scan direction was also found. A threshold intensity value for the production of laser induced surface ripples was calculated from a Gaussian analysis of measured track width. The threshold value when machining at 200 kHz, 750 mm/s, and 2 μJ was calculated to be 2.35 × 1014 W/m2.
Keywords: Fibre laser, stainless steel, picosecond, ultrashort pulse, surface structuring, laser induced periodic surface structures (LIPSS), laser process parameters