| 摘要 |
<p>An optical device having at least one optical element disposed on an optical path of an irradiation beam, wherein a first airtight room is defined along the optical path to shut off the optical path from the outside air and is filled with a specified gas; and the second airtight room is provided in the first airtight room to shut off the optical path from gas in the first airtight room and retain the optical element.</p> |
