Open Access

Additive manufacturing of optical elements out of polymer allow new design concepts for optics. The parts are built up layer by layer. Unlike polymer binding with glass particles with its sintering process no secondary step is necessary for polymer printing to create the final part. With more and more printers and transparent materials available, this technology becomes more and more relevant for prototyping or custom optics. Therefor a deep understanding of the optical effects in the part is desirable. Key property of optical elements is the refractive index. The materials for polymer printing are most commonly resins that cure under UV-exposure and show lower refractive indices in liquid phase than cured. Assuming a dependency of the refractive index on the grade of polymerization and therefor the UV-exposure, the layering process of additive manufacturing causes variations of the refractive index within the part. Using the Scanning Focused Refractive Index Microscopy, the distribution of the refractive index within and between the layers is analyzed. The analysis includes comparisons between raw parts after printing and parts after UV post curing. Additionally, layer free samples from a Continuous Liquid Interface Printing System are examined for the homogeneity of the refractive index distribution. The purpose of the presentation is to give a detailed insight into the optical effects occurring at the layer interfaces of elements created by additive manufacturing. Possible use cases of the refractive index distributions within the part are also discussed.