| 摘要 |
PROBLEM TO BE SOLVED: To provide an ArF excimer laser, which prevents efficiently impure gas from being mixed in the interiors of band narrowing boxes and a monitor box, and a band narrowing module of the excimer laser. SOLUTION: In an ArF excimer laser of a structure, wherein a purging unit 19 for purging pure inert gas is provided in the interior of at least either of a band narrowing box 11 housing optical elements 9A, 9B and 10 for narrowing the band of a laser beam 1 and a monitor box 16 housing optical elements 13A, 13B, 13C, 14 and 15 for measuring the characteristics of the laser beam 1, the purging unit 19 is provided with an impure gas sensor 27 for detecting the concentration of impure gas in at least some one out of an organic matter, ozone, water, oxygen and fluorine in the purged boxes 11 and 16 and a flow rate changing means 24 for changing the flow rate of the purged gas on the basis of the detected result of this concentration.
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