| 摘要 |
PROBLEM TO BE SOLVED: To prevent the contamination of a protective glass on the exit window of a laser-beam measuring apparatus as far as possible from the beginning and to eliminate a need of a cleaning operation, especially a cleaning operation before every measurement. SOLUTION: A compressed-air chamber 3 is arranged in front of a passage window for a laser beam. The compressed-air chamber is provided with a compressed-air connection part 4. The compressed-air connection part 4 is connected to a compressed-air source via a compressed-air conduit 5. When this apparatus is operated, compressed air is supplied to the compressed-air chamber 3. An air lock 6 is arranged on the side opposite to the passage window of the compressed-air chamber 3. In a state that the air lock is opened, a beam passage 7 is opened for the passage of the laser beam and for the laser beam reflected from an object 8 to be measured. In a state that the air lock is closed, the beam passage is closed. The air lock is opened only during a measurement.
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