In this work, a high-index silica-based fiber-optic mini-bundle sensor was constructed and implemented with a Fourier transform near-infrared spectrometer in the spectral region from 10 000 to 4500 cm-1. The refractive index of the multimode step index fiber was 1.618. This arrangement allows the propagation of waveguiding modes when the sensor is immersed in most resin systems. The reactions of a polyisocyanurate resin system and an epoxy resin system were monitored and peak assignments were made and discussed with respect to their potential for use in real-time analysis to be applied to cure control. Last, cure monitoring with this sensor was successfully demonstrated in a glass-reinforced resin transfer molded epoxy part.
Joy P. Dunkers, Kathleen M. Flynn, Mitchell T. Huang, and Walter G. McDonough, "Fourier Transform Near-Infrared Monitoring of Reacting Resins Using an Evanescent Wave High-Index Fiber-Optic Sensor," Appl. Spectrosc. 52, 552-556 (1998)