Measurement of wavefront variations to aid in situ refractive index calculations of a photopolymer under fabrication

The rise of additive manufacturing techniques in the field of optical elements has been a game changer from the perspective of flexibility and intricate complex designs. The excitement has also percolated to the field of fabricating functionalized optical elements with tailored optical properties like photoluminescence or refractive index control. However, it is an existing challenge to obtain precise control over the variations in refractive index, due to variations in the fabrication process itself, that are often, not always linear to quantify and comprehend. The research work presented in this paper was carried out with a proof of concept approach towards deducing the variations in the optical properties of a medium by monitoring light signals that pass through the sample. RI measurement using SFRIM technique has provided significant insight into the RI variations during and after the generation of optical elements in 2D. This work delves deeper into the intricacies of the refractive index changes in the polymer formed, in 3D voxels, from the wavefront measurements. A Shack Hartmann sensor is used to measure the wavefront of a collimated beam as it passes through a liquid resin sample as it undergoes UV based photocuring. The wavefront variations in the collimated beam is mapped as it interacts with the sample throughout the process As the first step in probing this technique, several UV masks were cured through resin films, and the wavefront variations noted before and after the process. It is seen that the wavefront map of the transmitted beam captures the optical path variations in the medium, which is clearly visible from the comparison of the wavefronts measured before and after the curing process.