Role of the intensity profile in femtosecond laser surface texturing: An experimental study

Abstract

Femtosecond Laser Induced Surface Structures evolve from ripples to spikes upon the increase of the energy dose Φ. Nevertheless, for a fixed Φ, several process parameters (pulse energy, repetition rate, average power, overlapping, etc.) play an important role in determining the resulting morphology. Here we show that the beam intensity profile Î as well has an important bearing on the structures morphology evolution. In the case of a Gaussian beam, Î has been modified by varying the beam size d. We observed that for a stationary beam, and for a Φ value, passing from d = 13 µm to d = 200 µm makes possible the transition from ripples to spikes. This transition is made energetically advantageous by using a Top Hat profile. Compared to a 200 µm wide Gaussian beam, a 62 µm wide Top Hat reduces by 10 the Φ required to yield a similar surface morphology (coexistence of spikes and micro-groves). Confirming these results over a large surface could further validate the shaping of Î as a key approach to both fully exploit the output power of state of the art, kW class, femtosecond laser whilst increasing the surface texturing throughput.

Keywords

• Texturing
• Blackening
• Ultra-short pulse laser
• Steel
• Beam shaping