Micro-optics manufacturing for automotive lighting applications: morphological and optical analysis of femtosecond laser milled samples

This thesis focuses on the milling procedures employed in the production of microscopic optical elements for automotive applications in rear lamp lighting, with a particular emphasis on the comparative analysis of the femtosecond laser technique offered by multiple suppliers and the standard cutter machining method. The femtosecond laser is able to manufacture micro-optics too small for the cutter. The aim of the study is to understand if this new machining process can outperform the already established cutter milling when both techniques can be applied. The two approaches are employed to mill a steel mould encompassing various optical elements utilized to achieve specific lighting effects within rear lamps. Following an injection moulding process, the final PMMA sample is obtained. The main work of the thesis consists in the analysis of these samples, with the aim of comparing the performance of various suppliers and different milling procedures. The benchmark for the optical properties of such samples is determined by optical simulations, specifically rendering techniques, using the CAD input specifications. The characterization process includes three main parts: morphological description through optical microscopy and profilometer analysis, and optical characterization by means of luminance camera measurements. The microscope imaging enables the examination of surface features, topography, and structural properties of the samples. Complementing this, the profilometer analysis extracts precise morphological information, including roughness measurements. To establish a correlation between the morphological and optical properties, roughness is modeled as a realization of a stochastic process. The optical characterization involves the use of luminance camera measurements to assess the performance and luminance distribution of the samples, offering valuable data pertaining to their optical functionality. Integrating the proposed roughness model into the optical simulations allows for a direct comparison between the simulated results and the luminance camera measurements. This comparative analysis helps validate the roughness model, while also providing a comprehensive assessment of the optical properties of the samples.