A new approach to Direct Laser Interference Patterning with scanner optics for high productivity

Surface texturing with laser beams is a versatile method able to process micrometric features on different materials. Commonly, in the direct writing mode a laser beam is moved by scanner optics over the surface to be textured. In this approach, despite the high quality of the obtainable micrometric pattern, the use of a diffraction limited beam with a size of the order of micrometers generates two limitations: i) inability to machine submicrometric features, and ii) low productivity on large areas. Direct laser interference patterning (DLIP) has been found to be a valid route for overcoming the feature size limitation. By using two or more interfering beams, the feature size can be decreased to sub-micrometric levels. Moreover, modelling of the interference pattern provides a higher process control than the one offered by other techniques, that work at sub-micro and nano level, such as laser induced periodic surface structures (LIPSS). However, traditional DLIP has not overcome the limit given by the poor productivity on large area. The optical arrangements used in DLIP technique is based on interferometric setups, which commonly require two or more beam paths converging on the processed zone. Accordingly, relative movement is given to the workpiece by means of linear stages, which reduces productivity compared to scanner optics. In this work, a new approach to DLIP is demonstrated, where interference patterns are processed using a scanner head. A nanosecond industrial laser source at 532 nm was used. The original beam was split in two. The interference was realized with a Michelson-Morley interferometric set-up. The interfering beams were then launched successfully into a conventional galvanometric scanner head, reflected by two mirrors and finally focused by an f-theta lens. Linear patterns were transferred to metallic surfaces with different periods in order to demonstrate the feasibility of the new system. At this initial phase, a texturing speed up to 500 mm/s was achieved, validating the capability and high productivity on large area fabrication.