**3. Results and Discussion**

## *3.1. Laser Surface Texturing*

In the first step, the required laser parameters for continuous surface texturing on 100Cr6 steel are determined. For the LSFL process, the laser fluence and the pulse overlap are optimized to generate a homogeneous LSFL-covered surface. Figure 2a shows the SEM image were the fluence is set to 0.5 J/cm2 and the pulse to pulse overlap for subsequent laser pulses and scanning lines is 80%. The use of the laser wavelength of 1030 nm and a linear polarization of the laser light results in a linear pattern with an average spatial periodicity of ≈900 nm. Due to the slightly smaller spatial period with respect to the laser wavelength and the perpendicular appearance of the structures, these LIPSS are identified as LSFL. The periodic structures show a uniform periodicity and a straight vertical course. The topographical shape is shown in Figure 2b by a AFM measurement. The height profile shows a homogeneous modulation depth of (201 ± 32) nm.

For the LBIA process the laser parameters and the scanning overlapp of the focused beam were adjusted to produce lines at a depth of approx. 1.6 to 1.7 μm. Due to the projection of lines of the grating interferometer onto the sample surface, the resulting surface structures are highly regular with a strict spatial periodicity of 1.5 μm. The resulting images of the SEM mesurements as well as the measured structural depth from AFM measurement is shown in Figure 2c,d.

The comparision between the LSFL and LBIA structures in Figure 2 shows that the LBIA structures show a higher uniformity and a much more pronounced orientation of the lines. The LSFL structures occur with a 0.6 times smaller spatial periodicity, while the modulation depth of the LBIA structures was about 8 times larger.

**Figure 2.** Laser-based surface modification using the LSFL and LBIA method. SEM image of LSFL (**a**) reveals a mostly vertical orientation of the structes and the corosponding AFM profile (**b**) shows the height profile. Structures fabricated by LBIA show a high homogeneity in the SEM image (**c**) and the AFM profile (**d**).
