Patent ID: 6781699
Filing Date: 2004-08-24
Classification: G01B

Abstract:
A scanning interferometer for measuring first and second surfaces of a test piece in sequence comprising:a test arm and a reference arm that convey test and reference beams of light; a beamsplitter within the test arm that separates the test beam into first and second sub-test beams; a focusing optic within the test arm that focuses the first and second sub-test beams to different points of focus; a compound probe within the test arm that conveys the first and second sub-test beams to the different points of focus; an actuator that relatively moves the probe with respect to the test piece between a first position at which: (a) the point of focus of the first sub-test beam is positioned on the first surface of the test piece and (b) the point of focus of the second sub-test beam is positioned off both the first and second surfaces of the test piece, and a second position at which: (a) the point of focus of the second sub-test beam is positioned on the second surface of the test piece and (b) the point of focus of the first sub-test beam is positioned off both the first and second surfaces of the test piece; and a detection system that detects interference signals between the reference beam and the first sub-test beam when the probe is located at the first position and detects interference signals between the reference beam and the second sub-test beam when the probe is located at the second position.