| 摘要 |
<P>PROBLEM TO BE SOLVED: To remove solid or wet foreign matters attached to the surface of an optical member to catch them without fail. Ž<P>SOLUTION: When an AC voltage with a predetermined frequency is applied to a comb shape electrode 405, respective portions close to the surface of an optical low-pass filter 401 are elliptically moved, to excite surface acoustic wave 410. When a foreign matter 411a exists on the surface of the optical low-pass filter 401, the foreign matter 411a is conveyed in the opposite direction of the advance direction (an arrow X in the figure) of the surface acoustic wave 410 by friction force to be generated by the elliptic movement of the surface acoustic wave 410, and caught by an absorption member 408. On the other hand, when a wet foreign matter 411b exists on the surface of the optical low-pass filter 401, the foreign matter 411b is conveyed in the advance direction (an arrow X in the figure) of the surface acoustic wave 410 by the radiation pressure of the surface acoustic wave 410, and caught by a water absorption member 409. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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