'Cold-air plasmas' - room-temperature gases of ionized air molecules - are widely used to kill dangerous bacteria, both in medical and food-processing environments. While the technique is good at dealing with antibiotic- and heat-resistant bacteria, the devices can be even more potent if the plasma is combined with an antibacterial chemical such as hydrogen peroxide. But understanding why this process occurs and how it could be improved is not easy because accurately measuring the relative abundances of different molecules in the stream - and how they interact - is tricky.

Researchers at the University of Colorado have shown that an optical-frequency comb can get round this problem to study molecules in the decontaminating stream. When light from the comb passes through the stream, the presence of a specific molecule or ion is signified by the absorption of a specific set of teeth. According to the team, the comb offers the unique capability of an extremely sensitive measurement and one that also yields information about the interaction dynamics, since many molecules can be simultaneously observed on short timescales.