Patent ID: 7130059

Claim:
A frequency-scanning interferometric measuring system for measuring topographical features of a test object comprising: a directional system for routing a measuring beam along a measurement path toward the test object; a reference element positioned along the measurement path adjacent to the test object in a fixed position with respect to the test object for distinguishing a reference beam portion of the measuring beam that acquires information concerning a surface of the reference element from an object beam portion of the measuring beam that acquires information concerning a diffuse surface of the test object; the directional system also providing for routing the information-laden object and reference beams along a common path toward a detector; the detector providing for detecting combined intensity variations of the information-laden object and reference beams as a comparison between the surfaces of the test object and the reference element; an imager that images interference patterns between the information-laden object and reference beams, wherein the information patterns are apparent as speckle patterns based at least in part on variations of the diffuse test object surface that exceed fringe intervals of the interference patterns; a frequency modifier that varies an effective frequency content of the object and reference beams detected by the detector; a processor that converts detected intensity variations induced by variations in the effective frequency content of the information-laden object and reference beams into measures of path length differences between the object and reference beams for measuring topographical features of the test object surface with respect to the reference element surface; and the processor being arranged for extracting from the effective frequency content of the information-laden object and reference beams relative modulation frequency measurements that distinguish profile variations between different transverse coordinates of the test object surface.