| 摘要 |
PROBLEM TO BE SOLVED: To accurately measure both a half-band width value, a 95%-integrated band width by inversely reflecting a spectral component of a diffused beam transmitted through an etalon and angularly separated and focusing it on a photodetector. SOLUTION: A laser beam 16 is contracted to 1/3 by a telescope 32 and irradiates a diffuser 34. The light scattered from the diffuser 34 irradiates an etalon 25, and a hollow retroreflector 38 returns the beam to the etalon 25 as a second pass. A component of the beam is accurately reflected to a second pass through the etalon 25 at 180 deg., and the reflected component is slightly displaced. A 45 deg.-mirror 40 which can sufficiently pass an input beam can be used to reflect the component after double passing through the etalon 25 for the displacement. The reflected component is focused at a focal distance of 1 m on a linear photodiode 44, and a fringe pattern 49 made of a plurality of peaks is detected.
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