Patent ID: 6710881
Filing Date: 2004-03-23
Classification: G01B

Abstract:
A system for high speed and precision measurement of the distance between at least two near contact surfaces, one of which is an optically transparent element and the other is a substantially non-transparent element using heterodyne interferometry, comprising:a laser source, which produces an output having two superimposed orthogonally polarized beams having S and P polarization, with a frequency difference between them; means for splitting the polarized beams into measurement and reference beams without altering the characteristics of the polarized beams; means for scanning the output of the laser source in both X and Y axes using an acousto optic deflector, wherein the two superimposed orthogonally polarized beams from the laser source enter the acoustic crystal of acoustic optic deflector Bragg's angle which produces a first order scanning beam and a zero order beam, both containing the two orthogonally polarized beams; means for causing the reference beams to interfere; a reference photo detector for detecting the reference beams and providing a reference signal; means for causing the measurement beam to strike the object of interest at an oblique angle after passing through a glass plate having a polarization coating on the bottom surface close to the object of interest, the oblique angle is such that the S polarization of the incident beam is reflected from the bottom surface of the polarization coated glass plate and the P polarization refracts through the glass plate, the P polarization reflects from the substantially non-transparent object of interest and refracts to the glass plate; means for causing the reflected S and P polarization beams from the bottom surface of the glass plate and the surface of the object respectively to interfere; a measurement photo detector for detecting the measurement beams and providing a measurement signal; and means for determining the distance between the bottom surface of the glass plate and the object surface based on the phase difference between the measurement and reference signals from the measurement and reference photo detectors.