## 3 Results and Discussion
### Industrial System for Direct Laser Interference Patterning  
In order to meet particular requirements of industrial environments, different concepts for interference structuring have been developed (see Figure 8a). The high-throughput DLIP module consist on optical system with a cylindrical telescope to expand the laser beam only in one direction, followed by an arrangement for beam splitting and alignment (patented by Fraunhofer IWS, Dresden). Later, a cylindrical lens is used for compressing the laser sub-beams, also only in one direction (details about this optical setup have been published elsewhere [41]). In this way, the module realizes beam shaping to a long drawn line in the focused area, where the interference pattern is obtained. Forming the interfering beams into the shape of long lines has advantages in achieving maximum process speeds. For instance, using a Q-switched slab-type solid-state laser, throughputs up to ~1 m\({}^{2}\)/min have been already achieved [25]. While conventional laser processing generates only one feature for each single pulse, DLIP allows the simultaneous fabrication of several hundred of features utilizing one single laser pulse. For example, in [25] 682 features were produced per single laser spot. For producing this amount of features using DLW (for example at 300 kHz repetition rate), to achieve feature densities y of ~10\({}^{9}\) m\({}^{-2}\), a maximum processing speed of 0.04 m\({}^{2}\)/min can be achieved using DLW. These speeds are about 10 to 50 times slower, compared to high-speed DLIP. Clearly, the use of laser systems operating in the MHz range could solve this problem. However, linear speeds over the limits of galvanometer scanners are required (>10 m/s) and simultaneously, the spot diameter over the work piece must be at least 8-10 \(\upmu\)m to be comparable with high-speed DLIP. Polygon-scanners are today capable to offer scanning speeds even over 100 m/s. However, their resolution is limited to 24-45 \(\upmu\)m (for IR radiation) [42].  
Other DLIP optical modules that have been developed enable an individualized control of structure properties (e.g., topographical structure geometry and period). These modules permit an automatized variation of the spatial period and geometry, and thus can be used to fabricate decorative elements.  
In recent years, various DLIP systems have been developed. In addition to the DLIP-\(\upmu\)FAB system (first prototype developed in 2013), a DLIP galvanometer scanning system was also recently constructed (Figure 8a). In this way, a significant improvement of the process speed due to the low inertia of the galvanometer mirrors compared to translational stages can be obtained. The scanner-based  
Figure 7: Profile of the structure formed by 2 beam DLIFs of substrate tilted by 45\({}^{\circ}\) and corresponding SEM images of the same area.  
DLIP optical head permits to reach throughputs of several cm\({}^{2}\) per min (e.g., 12 and 60 cm\({}^{2}\)/min for 2 and 10 KHz repetition rates). Furthermore, these optical heads have been already integrated into prototype system (DLIP-cube) as shown in Figure 8b. For the case when larger parts must be treated, a special DLIP system (developed at the TU-Dresden, Dresden, Germany) can be also used (Figure 8c). This system permits to treat cylindrical parts up to 600 mm in length and 300 mm in diameter. The system can be equipped with both ns and ps-laser systems and similarly like in the DLIP-\(\
u\)FAB system, different optical heads can be utilized. Further information about the 3D-DLIP system has been published elsewhere [43].