| 摘要 |
PROBLEM TO BE SOLVED: To obtain a measuring instrument that suspends measurement less frequently even if an object to be measured has small dust/dirt and scratches. SOLUTION: Two heterodyne beams having slightly different frequencies are guided to a measuring optical head 35 via a polarization surface storage optical fiber 34, and one portion of the heterodyne beams is taken out for interference to detect a reference beat signal. One of the remaining heterodyne beams is regularly reflected on a reference surface 41, the other beam is focused on a work W that is an object to be measured using an objective lens 39 having a numerical aperture (NA) that is equal to or more than the maximum surface inclination angle, and a measurement beat signal for allowing both beams returning by cat's eye reflection to interfere each other for detecting a measurement beat signal by a one-dimensional array sensor 44. The phase difference between the reference and measurement beat signals is calculated by a non- integration-type analog phase meter 48, and the interval between the measuring optical head 35 and the work W is controlled so that the phase difference between the calculated reference signal and the measurement signal becomes the same as the numeric value at a measurement start point.
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