An extreme ultraviolet light system includes an optical amplifier system and a catalytic conversion system. Each optical amplifier of the optical amplifier system includes a gain medium in the form of a gas mixture that produces an amplified light beam. The optical amplifier system includes a fluid input and a fluid output through which the gas mixture flows. The catalytic conversion system is fluidly connected to the fluid output of the optical amplifier system and to the fluid input of the optical amplifier system. The catalytic conversion system includes a catalytic converter that includes a housing; a substrate within the housing including openings through which the gas mixture can flow; and a catalyst applied as a coating to the interior surfaces of the openings of the substrate, the catalyst including particles of metal. The particles of metal can be nanoparticles of precious metal.