A method for extending the gas lifetime of an excimer laser by removing CF.sub.4 impurity, which comprises:a) reacting CF.sub.4, an undesirable impurity which forms and is contained in the lasing gases, with an amount of an oxidizing gas additive effective to produce one or more compounds which are condensible with refrigeration means, without reducing laser output below a predetermined acceptable level; andb) condensing said one or more compounds produced in step a) with refrigeration means, substantially without condensing said one or more rare gases therewith, thereby removing said CF.sub.4 impurity from said excimer laser and extending the gas lifetime of the laser.