The present invention is directed, in part, to a carbon dioxide laser resonator gas comprising carbon dioxide, helium, and nitrogen and having a total halocarbon concentration less than about 100 parts per trillion. In one embodiment, the total halocarbon concentration is less than about 50 parts per trillion. The laser resonator gases, laser systems, and methods of the present invention provide high efficiency and high power laser light while reducing the cost of maintenance and improving the performance of a laser system by limiting the total concentration of halocarbon.