| 摘要 |
<p>PURPOSE:To improve the measurement precision by detecting deviations of the position and the distribution of a reflected light due to the inclination of an object face to be irradiated and moving an object lens in the direction vertical to the optical axis in accordance with an error signal obtained from this detection output. CONSTITUTION:The light emitted from a Zeeman laser 9 having oscillation frequencies f1 and f2 is divided into lights of frequencies f2 and f1, which are polarized in two directions of polarization, by a lambda/4 plate 10. A beat frequency f1-f2 is detected by a photodetector 12. The light of f2 reaches a photodetector 15 by a polarizing prism 13. The light of f1 is reflected on the surface of an object 16 to be measured and is reflected totally by the polarizing prism 13 and reaches the photodetector 15. A beat frequency f1+DELTAf-f2 between frequencies f2 and f1+DELTAf is attained on the photodetector 15, and DELTAf is obtained on a basis of the difference between this beat frequency and the beat frequency f1-f2 obtained on the photodetector 12 and is integrated to obtain a displacement Z. The movement of an objective lens 20 in the Z-axis direction is measured by measuring the displacement of the object to be measured. Thus, the measurement precision is improved.</p> |
