*5.1. Deterministic Surface Textures and Groove Structures*

Deterministic surface textures made by direct laser structuring provide another practical method to control the surface functionality in general, and here in particular the frictional performance of tribological systems. Therewith, the surface feature characteristic can easily be adjusted by the chosen processing parameters, for instance, the laser beam spot size in the processing plane, the laser peak fluence of the irradiated pulses and the scan regime by the lateral pulse and line distance as well as the number of scan passes. As the width of the microscopic features can be varied by the pulse/line spacing, the scan number has a greater effect on the feature height. In particular, nanosecond lasers have been used during the past for the fabrication of high aspect-ratio surface features, among others, demonstrated in [52,53]. A recent study reports on the gradually increase of the friction coefficient with higher line density [54]. In any case, the fabrication of deterministic surface features with nanosecond lasers is characterized by strong material melting accompanied by a greater influence of the laser processing on the crystallographic structure, as observed up to 80 μm from the surface for the nanosecond laser regime [53]. This processing behavior can be a serious disadvantage that hinders the use of the cost-effective nanosecond laser technology for desired (micro-)engineering needs. A promising alternative therefore is provided by the ultrashort pulse laser technology, in particular for high-precision engineering applications. As a machining example, Figure 11 presents a number of different surface topographies made with an ultrashort pulse laser beam and a varied beam scanning pattern, such as (a) line pattern, (b) cross pattern and (c) a combination of an alternating line and crosswise scanned laser beam. The feature depth can easily be adjusted by the number of scan passes.

**Figure 11.** Deterministic surface textures made by ultrashort pulse laser processing under varied laser beam scanning procedures: (**a**) line pattern, (**b**) cross pattern and (**c**) alternating line and crosswise scanned laser beam.
