| 摘要 |
A method for determining the relative motion of a surface with respect to a measurement device, comprising:illuminating the surface with incident illumination, having a coherence length, such that the illumination is reflected from portions of the surface, wherein at least part of at least one of the incident and reflected illumination passes through a partially transmitting object that is part of the measuring device;detecting the illumination reflected from the surface, to generate a detected signal; anddetermining the relative motion of the surface parallel to the surface, from the detected signal,wherein the object and the surface are situated within a distance that is less than the coherence length of the detected illumination.
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