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

•Fs laser induced structures morphology strongly depends on beam intensity profile.•The flatter the profile the easier the evolution from LIPSS to spikes.•Top hat enables drastic reduction of dose yielding a given morphology. 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. [Display omitted]