Patent ID: 6317200
Filing Date: 2001-11-13
Classification: G01D,G01S

Abstract:
An apparatus for measuring the position of a measurement target, the apparatus comprising:a light source for producing a light beam;a first quarter-wave plate suitably placed to receive said light beam and to impart to it a desired first polarization;a first polarized beamsplitter suitably placed to receive and to redirect at least a portion of said light beam based on said first polarization toward the measurement target;a second quarter-wave plate suitably placed to receive said light beam and to impart to it a desired second polarization;a primary focusing lens suitably placed to receive and to focus said light beam to a focal point such that it has both a converging portion and a diverging portion;an opaque plate having an aperture, said plate being suitably placed to receive and to pass said converging portion through said aperture;a second non-polarized beamsplitter suitably placed to receive said light beam and to split it into an intensity sample portion and a target portion;a first detector focusing lens suitably placed to receive and to focus said intensity sample portion onto a first photodetector for detection of an intensity value;said second non-polarized beamsplitter being further suitably placed to receive said target portion when reflected from the measurement target and to split it into a reflectivity sample portion and a measurement portion;a second detector focusing lens suitably placed to receive and to focus said reflectivity sample portion onto a second photodetector for detection of a reflectivity value;said opaque plate being further suitably placed to receive said measurement portion and to pass a position portion through said aperture, such that said position portion is less in cross section than said measurement portion; andsaid second quarter-wave plate being further suitably placed to receive said position portion and to impart to it a desired third polarization; andsaid first polarized beamsplitter being further suitably placed to receive and to pass direct said position portion based on said third polarization onto a position sensitive detector for detection of a positional value, to permit use of said intensity value to normalize said positional value with respect to intensity of said light beam and use of said reflectivity value to normalize said positional value with respect to reflectivity of the measurement target.