Direct laser interference patterning combined with mask imaging

Direct laser interference patterning (DLIP) is a one step process to produce customized textured surfaces on the micrometer scale. Depending on the laser system, achieving a large area homogeneous pattern can be challenging. Particularly, with nanosecond lasers, an irregular intensity distribution or superposition leads to uneven melting, and an inhomogeneous surface structure. In this study, a robust methodology was developed, which allows the formation of a homogeneous pattern over a large area without these issues. A pulsed nanosecond laser with a clear diffraction influenced beam profile was used. The laser beam was split using a beam splitter, and the two beams were steered and superimposed by mirrors. A simple rectangular mask was used for beam shaping. Finally, the mask, together with an intermediate image of interference, were simultaneously projected onto a metal surface using a lens to create a homogeneous line pattern. Subsequent comparison with conventional DLIP method showed a significant reduction of surface defects, especially within the overlapping zones (over 90%). The proposed method retained the flexibility and advantages of a simple interference system.