| 摘要 |
PROBLEM TO BE SOLVED: To easily and quickly measure the beam diameters at plural points in the travel direction of a laser beam. SOLUTION: In this device, an optical grating member 12 which has an optical grating 6B consisting of grating lines with a prescribed pitch, and is disposed so that the direction of grating arrangement is tilted to the travel direction of a laser beam 5 to measure a beam diameter and the direction of the grating almost orthogonally crosses the travel direction of the laser beam 5, is displaced in the direction almost orthogonally crossing the travel direction of the laser beam 5 by a displacing means M, thereby displacing a position where the grating lines of the optical grating 6B crosses the laser beam 5 in the travel direction of the laser beam 5. Subsequently, the laser beam of which the intensity has been modulated by the grating lines of the optical grating 6B is receives to obtain wave-like signals, the beam diameter at the sequential position where the grating lines crosses the laser beam 5 is calculated by observation and operation means (9, 10) based on the maximum value and the minimum value in every one cycle of the wave-like signal.
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