| 摘要 |
PROBLEM TO BE SOLVED: To block dirt from being stuck on an optical window surface and to attain protection from damage caused by a falling object or the like by providing an air purge nozzle on the front face of the window surface so as to jet air upward from the window surface and generating an air current upward from the side of the window surface by jetting from the air purge nozzle. SOLUTION: A window surface 5 of an optical window 1 on an optical measuring instrument 3 is formed laterally long and along with the window surface 5 of the optical window 1, an air purge nozzle 7 is arranged. This air purge nozzle 7 has a nozzle port 9 for blowing curtain-shaped air over all the area of the window surface 5. Air jetted out of this nozzle port 9 generates an air current 10 upward from the side of the window surface 5. In this case, air is concretely jetted out of the nozzle port 9 away from the window surface 5 longer than about 10 mm at an angleθof about 30 deg. at a maximum so that the upward air current 10 can be provided.
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