Production of homogenous micro-structures by femtosecond laser micro-machining

• We have produced two types of homogenous micro-structures with a scanning femtosecond Gaussian laser beam on titanium.
• Two thermal ablation regimes have been identified that are responsible for the topology of the resulting micro-structures.
• The contribution of the line overlap and the intensity of the scanning line to feature formation and homogeneity has been investigated.
• We have shown that the line overlap has to be calculated based on the visually observed effective line width instead of the theoretical beam diameter.
• The resulting intensity profiles for overlapping Gaussian beams have been simulated in the context of the formation of homogenous arrays of micro-structures.

Two types of homogenous micro-structures have been produced by scanning femtosecond micro-machining at a repetition rate of 10 kHz. The contribution of line-intensity and line-overlap on the initial formation, the growth and the final feature dimensions has been investigated. Pillow-like structures are obtained at a wide range of line-overlap values and at moderate intensities. Bumpy structures have been produced at a tighter range of overlap and at higher intensities. The different resulting topologies have been explained with the existence of two different thermal ablation regimes. The simulation of the resulting intensity profiles has shown that homogenous pillow-like structures are obtained at a flat intensity profile, while homogenous bumpy structures are produced with a wavy profile. The effective beam diameter has to be determined visually from the width of a single line. Then the line-overlap is calculated based on the effective beam diameter to achieve homogenous structures.