When the high voltage power supply reaches its upper limit and laser power can no longer be maintained, the laser control computer performs automatic gas mixture adjustments. To compensate for halogen depletion, small amounts of halogen gas are injected into the laser vessel. Halogen injections increase laser output by increasing the amount of halogen available to form excimer species, increasing the laser gain. As impurities build up, halogen injections become less effective, since UV absorption gain loss becomes the predominant factor in lasing efficiency loss. At this point, a partial gas mixture replacement reduces the impurity concentration and restores proper lasing efficiency. At some point, even partial replenishments are ineffective. The laser then requires a complete gas exchange.
Gas mixture adjustments