Summary: Studies of the 355 nm laser induced free radical and cationic photopolymerization reactions of mono‐ and multifunctional monomers were conducted. These investigations were carried out with the aid of a specially constructed optical pyrometry instrument that provides rapid, reproducible temperature versus time profiles for these fast photopolymerization reactions. Using this technique, the effects of various reaction parameters and monomer structures on the rate and extent of the photopolymerization reactions were examined.Optical pyrometry instrument for the monitoring of laser‐induced photopolymerizations.magnified imageOptical pyrometry instrument for the monitoring of laser‐induced photopolymerizations.