Gradient periodic structures with feature sizes down to the micrometer range have gained attention since they can lead to anisotropic surface functions when produced on the surface of certain materials. Such kind of topographies can be produced for instance by using Direct Laser Interference Patterning (DLIP). However, fabrication of gradient surfaces with DLIP requires a careful synchronization of the motion of optical elements inside the laser configuration in order to dynamically adjust the interference angle. Due to mechanical and optical imperfections of the used components, an undesired waviness is introduced in the produced structures. The aim of this work is to develop an improved manufacturing strategy of periodic gradient surface structures with minimum errors.

By using a two-beam DLIP configuration, with a 10 ps laser operating at 1064 nm wavelength, interfering laser pulses were systematically monitored and captured by a CCD camera when applying different interfering angles. The captured images reveal absolute deviations of the pattern locations up to 10 µm with respect to the starting position as well as relative deviations between adjacent pulses ranging from -3.5 to 3.6 µm. The absolute deviations are mainly attributed to the geometrical asymmetry of optical elements. In comparison, the relative deviations show an unpredictable distribution, which can be ascribed to the mechanical vibration during the production of the gradient structures. Mechanical fixation and movement offsets strategies are designed on the basis of aforementioned results to minimize the negative impacts of the previous laser configuration. After adopting the optimized strategy, both the absolute and relative deviations are reduced to -3.4 to 3.5 µm, and the quantity of pulses with a low relative deviation between ±1.0 µm also increases by 19.4% compared to the original strategy.