Abstract: A halogen generator which uses a material which absorbs commercially available halogen and, on being heated, releases the halogen in a very pure form, i.e. >99.7%. Such a generator can be used in a gas management system for an excimer laser in which the laser gas contains a halogen donor, an active rare gas and an inert gas diluent. Cleaners are provided to enable the removal from the laser gas mixture of contaminants which build up in operation of the laser and the halogen gas generator is provided to replace halogen lost in the contaminants and elsewhere. The generator can be operated even when the laser is in operation so that a desired partial pressure of the halogen can be maintained.