| 摘要 |
<p>The optical path difference between two reflecting surfaces of an etalon 2 is monitored by directing a light beam B onto the etalon, directing the reflected beam Ba from the etalon onto an optical reference wedge 3 and directing the reflected beam Bb from the wedge onto a linear photo-detector array 4. The position along the array 4 of a peak of light intensity represent the location of an interference maximum and corresponds to reflection of light at that position along the length L of the wedge 3 at which the optical path difference of the wedge equals the optical path difference of the etalon being measured. The etalon 2 may comprise a data carrier encoded by variations in its relief (and therefore in its optical path difference), which data carrier may comprise a rotatable disc and the apparatus may comprise an optical head movable radially of the disc to read different concentric tracks.</p> |
