Photopolymerising resin becomes solid during polymerization by bridging monomers when the resin absorbs light energy. We can evaluate the cure extent and measure the amount of monomer and initiator in the resin by using Raman spectroscopy. The figure shows a Raman spectrum of resin before UV irradiation, after 105 minutes of UV irradiation and after 205 minutes of UV irradiation. The cure extent (right graph) is calculated from the ratio of the intensity at 1640 cm-1(monomer) and 1598 cm-1(initiator).