The disclosure relates to the removal of hydrogen fluoride (HF) from an excimer laser either in operation or in standby using a metal halide salt reactor. Removal of HF is desirable because the contaminant not only absorbs laser emission, thus reducing laser power, but it is also chemically reactive, and degrades the lifetime of internal laser components. The metal halide salt reactor may be provided either in the laser vessel or in an external conduit loop.