| 摘要 |
Two optical beams of different frequencies are focussed as concentric spots, one spot being larger than the other, on a reflective surface whose roughness is to be measured. The smaller spot has a maximum dimension that is smaller than any significant deviation of the profile of the surface from spatial uniformity, and the larger spot has a minimum dimension that is larger than any significant deviation of the surface profile from spatial uniformity. The two beams are reflected from the surface along a common path with a phase difference that is measured by a heterodyne interferometric technique. The phase difference measurement is indicative of the roughness of the surface, and is substantially insensitive to vibration of the surface.
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