Projection lighting are widely used for different applications such as ambiance lighting, or safety lighting, enabling having clear projected pieces of information on the ground or on walls. The research and innovation activities related to their manufacturing target the improvement of the lighting quality and details while keeping low manufacturing cost. Indeed, those lenses are made of polymer which are injected into moulds. A way to improve projection lighting is therefore to improve the mould manufacturing, and this paper will describe how to manufacture them with a high quality thanks to a femto-second laser based process.

Replication of micrometer-scale patterns on steel has been performed using a 1030nm 300fs laser. The objective of the experiment is the generation of Fresnel-lenses style gutters. The set-up includes a high Numerical Aperture (NA) microscope objective in order to get very small (10 to 20micrometers) beam shape in the processing sample. In order to get the optimal profile on the mould a very specific beam shape is being studied thanks to the use a a fully reflective beam shaper based on MPLC (Multi-Plane Light Conversion) technology. The beam shaper delivers a triangular shape with a high sharpness : sharpness of 1/5 and 1/10 has been successfully installed on the processing set-up through the high NA objectives as shown on Figure 1. The beam shaper includes a mode-cleaning feature in order to stabilize the laser output and get a stable shape during the process.

Processing on steel of specific gutters at the micrometre scale has been demonstrated with the targeted wall slope as shown on Figure 2. The samples are characterized using an optical profilometer, including the gutters depth, wall slopes, and roughness.