| 摘要 |
PROBLEM TO BE SOLVED: To surely prevent an optical system from increasing in the inside pressure, while a specific gas is being supplied. SOLUTION: A specific gas (for instance, nitrogen gas) is supplied from a gas supply feed device through the intermediary of feed paths 58, 60, and 62 to an optical system PL which is arranged in the optical path of a lighting beam. Solenoid valves 80, 97, and 88 which open/close branching paths 78, 99, and 86 provided to the feed paths 58, 60, and 62 are opened by a control device, when the pressure of specific gas exceeds a prescribed value while specific gas is being supplied. With this setup, an optical system can be surely prevented from increasing in the inside pressure while a specific gas is being supplied.
|
