In-Process Measurement of Resin’s Curing Degree in Micro-Stereolithography Using Internal Reflection at Critical angle

Abstract

Micro-stereolithography has been proposed to fabricate resin in arbitrary structures using optical energy. This technique is essentially based on the polymerization feature of photosensitive resin. Once original resin is cured by light in a specific wavelength range, polymerization reaction will start and resin’s state will turn from liquid to solid. The curing degree of resin determines the solidification degree of products and also largely impacts final fabrication qualities. Therefore, an in-process measurement that monitors states of resin and provides the possibility of feedback in a fabrication system shows a great significance. However, so far there are seldom investigations on curing degree in micro-stereolithograpahy. In our research, we raised a measurement method that utilizes the variation of resin’s refractive index in polymerization and the high refractive-index sensitivity of internal reflection at the critical angle. The feasibility of this method has been confirmed by using simulations based on the rigorous coupled-wave analysis (RCWA) method. In our experiment work, curing process of resin has been successfully monitored and recorded. The formation and variation of curd resin has been directly observed. The distribution of refractive index was calculated according to the grey value of reflection distribution. Our research will be a start point of in-process measurement in micro-stereolithography. Fabrication systems with in-process measurement functions will be wildly investigated in the future.