Monitoring of silicon suboxide activity is an important parameter in experiments relevant for silicon metal production. In previous work a reactor with optical access to the reaction zone, by use of a sequence of sapphire, UV fused silica and IR transparent sapphire and CaF2 windows, was designed. It was found that at temperatures below 2000 K, thermal excitation of silicon suboxide does not provide sufficient emission intensity for analytical purposes. In this work, this has been remedied by applying incident light of 266 nm from a laser as additional energy for molecular excitation. The resulting fluorescence was used to qualify and quantify silicon monoxide inside the reactor. The silicon monoxide was generated from a heated charge of silicon dioxide and silicon carbide. Experiments with silicon dioxide charge and reducing agent in the form of a methane/hydrogen gas mixture was also conducted. Off-gas analysis was performed with IR spectroscopy.