Patent ID: 6246482
Filing Date: 2001-06-12
Classification: G01B,G01D,G01P,G01S,G06F

Abstract:
A method for determining the relative motion of a surface with respect to a measurement device comprising:illuminating the surface with incident illumination such that illumination is reflected from portions of the surface;placing a partially reflecting or diffracting object, which is part of the measuring device, adjacent to the surface, wherein part of the incident illumination is reflected or diffracted by the object, as a reference illumination;coherently detecting the illumination reflected from the surface, utilizing the illumination reflected from or diffracted by the object as a local oscillator, to form a signal;determining the relative motion of the surface from the signal;varying the phase of the illumination reflected from or diffracted by the object with respect to that reflected from the surface; anddetermining the direction of relative motion parallel to the surface based on a characteristic of the signal caused by said varied relative phase.